diff --git a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/laserDTRM/laserDTRM.C b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/laserDTRM/laserDTRM.C
index ae930a1e39..6524c571ae 100644
--- a/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/laserDTRM/laserDTRM.C
+++ b/applications/solvers/multiphase/icoReactingMultiphaseInterFoam/laserDTRM/laserDTRM.C
@@ -329,7 +329,7 @@ Foam::radiation::laserDTRM::laserDTRM(const volScalarField& T)
 :
     radiationModel(typeName, T),
     mode_(powerDistNames_.get("mode", *this)),
-    DTRMCloud_(mesh_, "DTRMCloud", IDLList<DTRMParticle>()),
+    DTRMCloud_(mesh_, Foam::zero{}, "DTRMCloud"),  // Empty cloud
     nParticles_(0),
     ndTheta_(get<label>("nTheta")),
     ndr_(get<label>("nr")),
@@ -427,7 +427,7 @@ Foam::radiation::laserDTRM::laserDTRM
 :
     radiationModel(typeName, dict, T),
     mode_(powerDistNames_.get("mode", *this)),
-    DTRMCloud_(mesh_, "DTRMCloud", IDLList<DTRMParticle>()),
+    DTRMCloud_(mesh_, Foam::zero{}, "DTRMCloud"),  // Empty cloud
     nParticles_(0),
     ndTheta_(get<label>("nTheta")),
     ndr_(get<label>("nr")),
diff --git a/applications/test/passiveParticle/Make/files b/applications/test/passiveParticle/Make/files
index 43afc08055..4bce2d4994 100644
--- a/applications/test/passiveParticle/Make/files
+++ b/applications/test/passiveParticle/Make/files
@@ -1,3 +1,3 @@
-Test-passiveParticle.C
+Test-passiveParticle.cxx
 
 EXE = $(FOAM_USER_APPBIN)/Test-passiveParticle
diff --git a/applications/test/passiveParticle/Test-passiveParticle.C b/applications/test/passiveParticle/Test-passiveParticle.cxx
similarity index 94%
rename from applications/test/passiveParticle/Test-passiveParticle.C
rename to applications/test/passiveParticle/Test-passiveParticle.cxx
index 3f9487ca58..fb0ce5e0de 100644
--- a/applications/test/passiveParticle/Test-passiveParticle.C
+++ b/applications/test/passiveParticle/Test-passiveParticle.cxx
@@ -24,7 +24,7 @@ License
     along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
 
 Application
-    testPassiveParticle
+    Test-passiveParticle
 
 Description
     Test cloud of passive particles.
@@ -50,12 +50,8 @@ int main(int argc, char *argv[])
 
     {
         // Start with empty cloud
-        passiveParticleCloud particles
-        (
-            mesh,
-            cloudName,
-            IDLList<passiveParticle>()
-        );
+        passiveParticleCloud particles(mesh, Foam::zero{}, cloudName);
+
         Pout<< "Starting particles:" << particles.size() << endl;
 
         Pout<< "Adding a particle." << endl;
diff --git a/applications/utilities/parallelProcessing/redistributePar/parLagrangianDistributor.C b/applications/utilities/parallelProcessing/redistributePar/parLagrangianDistributor.C
index 626cb9c642..908a7e3610 100644
--- a/applications/utilities/parallelProcessing/redistributePar/parLagrangianDistributor.C
+++ b/applications/utilities/parallelProcessing/redistributePar/parLagrangianDistributor.C
@@ -227,19 +227,21 @@ Foam::parLagrangianDistributor::distributeLagrangianPositions
     pBufs.finishedSends();
 
 
+    // The cloud name
+    const word cloudName = lpi.name();
+
     {
         // Temporarily rename original cloud so we can construct a new one
         // (to distribute the positions) without getting a duplicate
         // registration warning
-        const word cloudName = lpi.name();
         lpi.rename(cloudName + "_old");
 
-        // New cloud on tgtMesh
+        // New empty cloud on tgtMesh
         passivePositionParticleCloud lagrangianPositions
         (
             tgtMesh_,
-            cloudName,
-            IDLList<passivePositionParticle>()
+            Foam::zero{},
+            cloudName
         );
 
         // Retrieve from receive buffers
@@ -310,11 +312,11 @@ Foam::parLagrangianDistributor::distributeLagrangianPositions
         //        ).objectPath()
         //    );
         //}
-
-        // Restore cloud name
-        lpi.rename(cloudName);
     }
 
+    // Restore cloud name
+    lpi.rename(cloudName);
+
 
     // The constructMap is in linear (processor) order
     return autoPtr<mapDistributeBase>::New
diff --git a/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.C b/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.C
index dd6ba34e55..95416aecd1 100644
--- a/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.C
+++ b/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -34,6 +34,7 @@ namespace Foam
     defineTemplateTypeNameAndDebug(Cloud<passivePositionParticle>, 0);
 }
 
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 Foam::passivePositionParticleCloud::passivePositionParticleCloud
@@ -52,15 +53,4 @@ Foam::passivePositionParticleCloud::passivePositionParticleCloud
 }
 
 
-Foam::passivePositionParticleCloud::passivePositionParticleCloud
-(
-    const polyMesh& mesh,
-    const word& cloudName,
-    const IDLList<passivePositionParticle>& particles
-)
-:
-    Cloud<passivePositionParticle>(mesh, cloudName, particles)
-{}
-
-
 // ************************************************************************* //
diff --git a/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.H b/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.H
index 2ac7f757ed..86aac80056 100644
--- a/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.H
+++ b/applications/utilities/parallelProcessing/redistributePar/passivePositionParticleCloud.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2017-2019 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef passivePositionParticleCloud_H
-#define passivePositionParticleCloud_H
+#ifndef Foam_passivePositionParticleCloud_H
+#define Foam_passivePositionParticleCloud_H
 
 #include "Cloud.H"
 #include "passivePositionParticle.H"
@@ -53,23 +53,21 @@ class passivePositionParticleCloud
 :
     public Cloud<passivePositionParticle>
 {
-    // Private Member Functions
-
-        //- No copy construct
-        passivePositionParticleCloud
-        (
-            const passivePositionParticleCloud&
-        ) = delete;
-
-        //- No copy assignment
-        void operator=(const passivePositionParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef passivePositionParticle parcelType;
+
+    //- No copy construct
+    passivePositionParticleCloud(const passivePositionParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const passivePositionParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit passivePositionParticleCloud
         (
             const polyMesh& mesh,
@@ -77,13 +75,16 @@ public:
             bool readFields = true
         );
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         passivePositionParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<passivePositionParticle>& particles
-        );
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<passivePositionParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/applications/utilities/parallelProcessing/redistributePar/unmappedPassivePositionParticleCloud.H b/applications/utilities/parallelProcessing/redistributePar/unmappedPassivePositionParticleCloud.H
index 031e04801c..0ac69d6f94 100644
--- a/applications/utilities/parallelProcessing/redistributePar/unmappedPassivePositionParticleCloud.H
+++ b/applications/utilities/parallelProcessing/redistributePar/unmappedPassivePositionParticleCloud.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2015 OpenFOAM Foundation
-    Copyright (C) 2019-2020 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -36,8 +36,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef unmappedPassivePositionParticleCloud_H
-#define unmappedPassivePositionParticleCloud_H
+#ifndef Foam_unmappedPassivePositionParticleCloud_H
+#define Foam_unmappedPassivePositionParticleCloud_H
 
 #include "passivePositionParticleCloud.H"
 
@@ -54,12 +54,11 @@ class unmappedPassivePositionParticleCloud
 :
     public passivePositionParticleCloud
 {
-
 public:
 
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit unmappedPassivePositionParticleCloud
         (
             const polyMesh& mesh,
@@ -70,15 +69,15 @@ public:
             passivePositionParticleCloud(mesh, cloudName, readFields)
         {}
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         unmappedPassivePositionParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<passivePositionParticle>& particles
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
         )
         :
-            passivePositionParticleCloud(mesh, cloudName, particles)
+            passivePositionParticleCloud(mesh, Foam::zero{}, cloudName)
         {}
 
 
@@ -89,7 +88,7 @@ public:
     // Member Functions
 
         //- Switch off remapping of cells of particles when
-        //  mesh topology changes
+        //- mesh topology changes
         virtual void autoMap(const mapPolyMesh&)
         {}
 
diff --git a/applications/utilities/preProcessing/mapFields/mapLagrangian.C b/applications/utilities/preProcessing/mapFields/mapLagrangian.C
index 9f712a5df4..88989a9d22 100644
--- a/applications/utilities/preProcessing/mapFields/mapLagrangian.C
+++ b/applications/utilities/preProcessing/mapFields/mapLagrangian.C
@@ -133,6 +133,7 @@ void mapLagrangian(const meshToMesh0& meshToMesh0Interp)
                 cloudDir,
                 false
             );
+
             Info<< "    read " << sourceParcels.size()
                 << " parcels from source mesh." << endl;
 
@@ -140,8 +141,8 @@ void mapLagrangian(const meshToMesh0& meshToMesh0Interp)
             passiveParticleCloud targetParcels
             (
                 meshTarget,
-                cloudDir,
-                IDLList<passiveParticle>()
+                Foam::zero{},
+                cloudDir
             );
 
             passiveParticle::trackingData td(targetParcels);
diff --git a/applications/utilities/preProcessing/mapFieldsPar/mapLagrangian.C b/applications/utilities/preProcessing/mapFieldsPar/mapLagrangian.C
index dc9735628b..9518d7594f 100644
--- a/applications/utilities/preProcessing/mapFieldsPar/mapLagrangian.C
+++ b/applications/utilities/preProcessing/mapFieldsPar/mapLagrangian.C
@@ -129,6 +129,7 @@ void mapLagrangian(const meshToMesh& interp)
                 cloudDir,
                 false
             );
+
             Info<< "    read " << sourceParcels.size()
                 << " parcels from source mesh." << endl;
 
@@ -136,8 +137,8 @@ void mapLagrangian(const meshToMesh& interp)
             passiveParticleCloud targetParcels
             (
                 meshTarget,
-                cloudDir,
-                IDLList<passiveParticle>()
+                Foam::zero{},
+                cloudDir
             );
 
             passiveParticle::trackingData td(targetParcels);
diff --git a/src/OpenFOAM/fields/cloud/cloud.C b/src/OpenFOAM/fields/cloud/cloud.C
index 6fec765fcc..d9e9c947de 100644
--- a/src/OpenFOAM/fields/cloud/cloud.C
+++ b/src/OpenFOAM/fields/cloud/cloud.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2016-2019 OpenCFD Ltd.
+    Copyright (C) 2016-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -37,6 +37,7 @@ namespace Foam
 }
 
 const Foam::word Foam::cloud::prefix("lagrangian");
+
 Foam::word Foam::cloud::defaultName("defaultCloud");
 
 const Foam::Enum<Foam::cloud::geometryType>
@@ -51,7 +52,7 @@ Foam::cloud::geometryTypeNames
 
 Foam::cloud::cloud(const objectRegistry& obr)
 :
-    cloud(obr, defaultName)
+    cloud(obr, cloud::defaultName)
 {}
 
 
@@ -61,12 +62,13 @@ Foam::cloud::cloud(const objectRegistry& obr, const word& cloudName)
     (
         IOobject
         (
-            cloudName,
+            (cloudName.empty() ? cloud::defaultName : cloudName),
             obr.time().timeName(),
-            prefix,
+            cloud::prefix,
             obr,
             IOobject::NO_READ,
-            IOobject::AUTO_WRITE
+            IOobject::AUTO_WRITE,
+            IOobject::REGISTER
         )
     )
 {}
diff --git a/src/OpenFOAM/fields/cloud/cloud.H b/src/OpenFOAM/fields/cloud/cloud.H
index 86f2a0472a..ed1109cdea 100644
--- a/src/OpenFOAM/fields/cloud/cloud.H
+++ b/src/OpenFOAM/fields/cloud/cloud.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef cloud_H
-#define cloud_H
+#ifndef Foam_cloud_H
+#define Foam_cloud_H
 
 #include "objectRegistry.H"
 #include "Enum.H"
@@ -59,16 +59,6 @@ class cloud
 :
     public objectRegistry
 {
-
-    // Private Member Functions
-
-        //- No copy construct
-        cloud(const cloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const cloud&) = delete;
-
-
 public:
 
     //- Cloud geometry type (internal or IO representations)
@@ -78,11 +68,11 @@ public:
         POSITIONS       //!< positions
     };
 
+    //- Named enumerations "coordinates", "positions"
     static const Enum<geometryType> geometryTypeNames;
 
 
-    //- Runtime type information
-    TypeName("cloud");
+    // Static Data Members
 
         //- The prefix to local: %lagrangian
         static const word prefix;
@@ -91,12 +81,25 @@ public:
         static word defaultName;
 
 
+    //- Runtime type information
+    TypeName("cloud");
+
+
+    // Generated Methods
+
+        //- No copy construct
+        cloud(const cloud&) = delete;
+
+        //- No copy assignment
+        void operator=(const cloud&) = delete;
+
+
     // Constructors
 
-        //- Construct for given objectRegistry and default cloud name
+        //- Construct for given objectRegistry. Uses default cloud name
         explicit cloud(const objectRegistry& obr);
 
-        //- Construct for given objectRegistry and named cloud instance
+        //- Construct for given objectRegistry and named cloud
         cloud(const objectRegistry& obr, const word& cloudName);
 
 
@@ -139,7 +142,7 @@ public:
             //- Locate an IOField within object registry
             //  \return nullptr if not found or wrong type
             template<class Type>
-            inline static const IOField<Type>* findIOField
+            static const IOField<Type>* findIOField
             (
                 const word& fieldName,
                 const objectRegistry& obr
@@ -150,7 +153,7 @@ public:
 
             //- Locate the "position" IOField within object registry
             //  \return nullptr if not found or wrong type
-            inline static const IOField<point>* findIOPosition
+            static const IOField<point>* findIOPosition
             (
                 const objectRegistry& obr
             )
@@ -161,7 +164,7 @@ public:
             //- Lookup an IOField within object registry
             //  Fatal if not found or wrong type
             template<class Type>
-            inline static const IOField<Type>& lookupIOField
+            static const IOField<Type>& lookupIOField
             (
                 const word& fieldName,
                 const objectRegistry& obr
diff --git a/src/functionObjects/field/nearWallFields/nearWallFields.C b/src/functionObjects/field/nearWallFields/nearWallFields.C
index 45c0a87c13..efd3f273ec 100644
--- a/src/functionObjects/field/nearWallFields/nearWallFields.C
+++ b/src/functionObjects/field/nearWallFields/nearWallFields.C
@@ -61,13 +61,8 @@ void Foam::functionObjects::nearWallFields::calcAddressing()
 
     DebugInFunction << "nPatchFaces: " << globalWalls.totalSize() << endl;
 
-    // Construct cloud
-    Cloud<findCellParticle> cloud
-    (
-        mesh_,
-        cloud::defaultName,
-        IDLList<findCellParticle>()
-    );
+    // Start with empty cloud
+    Cloud<findCellParticle> cloud(mesh_, Foam::zero{}, cloud::defaultName);
 
     // Add particles to track to sample locations
     nPatchFaces = 0;
diff --git a/src/functionObjects/field/streamLine/streamLine.C b/src/functionObjects/field/streamLine/streamLine.C
index b93ffe9f7f..e8cf00d6c1 100644
--- a/src/functionObjects/field/streamLine/streamLine.C
+++ b/src/functionObjects/field/streamLine/streamLine.C
@@ -47,13 +47,8 @@ namespace functionObjects
 
 void Foam::functionObjects::streamLine::track()
 {
-    IDLList<streamLineParticle> initialParticles;
-    streamLineParticleCloud particles
-    (
-        mesh_,
-        cloudName_,
-        initialParticles
-    );
+    // Start with empty cloud
+    streamLineParticleCloud particles(mesh_, Foam::zero{}, cloudName_);
 
     const sampledSet& seedPoints = sampledSetPoints();
 
diff --git a/src/functionObjects/field/streamLine/streamLineParticleCloud.C b/src/functionObjects/field/streamLine/streamLineParticleCloud.C
index 7521b51ffd..005e180172 100644
--- a/src/functionObjects/field/streamLine/streamLineParticleCloud.C
+++ b/src/functionObjects/field/streamLine/streamLineParticleCloud.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
+    Copyright (C) 2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -53,15 +54,4 @@ Foam::streamLineParticleCloud::streamLineParticleCloud
 }
 
 
-Foam::streamLineParticleCloud::streamLineParticleCloud
-(
-    const polyMesh& mesh,
-    const word& cloudName,
-    const IDLList<streamLineParticle>& particles
-)
-:
-    Cloud<streamLineParticle>(mesh, cloudName, particles)
-{}
-
-
 // ************************************************************************* //
diff --git a/src/functionObjects/field/streamLine/streamLineParticleCloud.H b/src/functionObjects/field/streamLine/streamLineParticleCloud.H
index 4ec5383c6c..02a8aa15ad 100644
--- a/src/functionObjects/field/streamLine/streamLineParticleCloud.H
+++ b/src/functionObjects/field/streamLine/streamLineParticleCloud.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019-2022 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -56,22 +56,19 @@ class streamLineParticleCloud
 {
 public:
 
-    //- Type of parcel the cloud was instantiated for
+    //- Type of parcel within the cloud
     typedef streamLineParticle parcelType;
 
+    //- No copy construct
+    streamLineParticleCloud(const streamLineParticleCloud&) = delete;
 
-    // Generated Methods
-
-        //- No copy construct
-        streamLineParticleCloud(const streamLineParticleCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const streamLineParticleCloud&) = delete;
+    //- No copy assignment
+    void operator=(const streamLineParticleCloud&) = delete;
 
 
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit streamLineParticleCloud
         (
             const polyMesh& mesh,
@@ -79,13 +76,16 @@ public:
             bool readFields = true
         );
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         streamLineParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<streamLineParticle>& particles
-        );
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<streamLineParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLine.C b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLine.C
index 8125a777b3..cb6fabaf84 100644
--- a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLine.C
+++ b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLine.C
@@ -142,12 +142,11 @@ void Foam::functionObjects::wallBoundedStreamLine::track()
     // Find nearest wall particle for the seedPoints
     // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-    IDLList<wallBoundedStreamLineParticle> initialParticles;
     wallBoundedStreamLineParticleCloud particles
     (
         mesh_,
-        cloudName_,
-        initialParticles
+        Foam::zero{},
+        cloudName_
     );
 
     {
diff --git a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.C b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.C
index 9d1a1e6a12..04242102ea 100644
--- a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.C
+++ b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.C
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
+    Copyright (C) 2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,15 +53,4 @@ Foam::wallBoundedStreamLineParticleCloud::wallBoundedStreamLineParticleCloud
 }
 
 
-Foam::wallBoundedStreamLineParticleCloud::wallBoundedStreamLineParticleCloud
-(
-    const polyMesh& mesh,
-    const word& cloudName,
-    const IDLList<wallBoundedStreamLineParticle>& particles
-)
-:
-    Cloud<wallBoundedStreamLineParticle>(mesh, cloudName, particles)
-{}
-
-
 // ************************************************************************* //
diff --git a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.H b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.H
index 69ef36d9ba..d95b093bf5 100644
--- a/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.H
+++ b/src/functionObjects/field/wallBoundedStreamLine/wallBoundedStreamLineParticleCloud.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -28,7 +28,7 @@ Class
     Foam::wallBoundedStreamLineParticleCloud
 
 Description
-    A Cloud of streamLine particles
+    A Cloud of wall-bounded streamLine particles
 
 SourceFiles
     streamLineCloud.C
@@ -56,10 +56,9 @@ class wallBoundedStreamLineParticleCloud
 {
 public:
 
-    //- Type of parcel the cloud was instantiated for
+    //- Type of parcel within the cloud
     typedef wallBoundedStreamLineParticle parcelType;
 
-
     // Generated Methods
 
         //- No copy construct
@@ -74,7 +73,7 @@ public:
 
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit wallBoundedStreamLineParticleCloud
         (
             const polyMesh& mesh,
@@ -82,13 +81,16 @@ public:
             bool readFields = true
         );
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         wallBoundedStreamLineParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<wallBoundedStreamLineParticle>& particles
-        );
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<wallBoundedStreamLineParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/src/lagrangian/basic/Cloud/Cloud.C b/src/lagrangian/basic/Cloud/Cloud.C
index 18741d9623..eb15d60699 100644
--- a/src/lagrangian/basic/Cloud/Cloud.C
+++ b/src/lagrangian/basic/Cloud/Cloud.C
@@ -59,6 +59,25 @@ void Foam::Cloud<ParticleType>::checkPatches() const
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
+template<class ParticleType>
+Foam::Cloud<ParticleType>::Cloud
+(
+    const polyMesh& pMesh,
+    const Foam::zero,
+    const word& cloudName
+)
+:
+    cloud(pMesh, cloudName),
+    polyMesh_(pMesh),
+    geometryType_(cloud::geometryType::COORDINATES)
+{
+    checkPatches();
+
+    (void)polyMesh_.tetBasePtIs();
+    (void)polyMesh_.oldCellCentres();
+}
+
+
 template<class ParticleType>
 Foam::Cloud<ParticleType>::Cloud
 (
@@ -67,21 +86,8 @@ Foam::Cloud<ParticleType>::Cloud
     const IDLList<ParticleType>& particles
 )
 :
-    cloud(pMesh, cloudName),
-    IDLList<ParticleType>(),
-    polyMesh_(pMesh),
-    labels_(),
-    globalPositionsPtr_(),
-    geometryType_(cloud::geometryType::COORDINATES)
+    Cloud<ParticleType>(pMesh, Foam::zero{}, cloudName)
 {
-    checkPatches();
-    (void)polyMesh_.oldCellCentres();
-
-    // Ask for the tetBasePtIs to trigger all processors to build
-    // them, otherwise, if some processors have no particles then
-    // there is a comms mismatch.
-    (void)polyMesh_.tetBasePtIs();
-
     if (particles.size())
     {
         IDLList<ParticleType>::operator=(particles);
diff --git a/src/lagrangian/basic/Cloud/Cloud.H b/src/lagrangian/basic/Cloud/Cloud.H
index 44696ae669..9bc8e5c37d 100644
--- a/src/lagrangian/basic/Cloud/Cloud.H
+++ b/src/lagrangian/basic/Cloud/Cloud.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2022 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -67,7 +67,7 @@ class Cloud
     public cloud,
     public IDLList<ParticleType>
 {
-    // Private data
+    // Private Data
 
         //- Reference to the mesh database
         const polyMesh& polyMesh_;
@@ -130,6 +130,14 @@ public:
 
     // Constructors
 
+        //- Construct without particles
+        Cloud
+        (
+            const polyMesh& mesh,
+            const Foam::zero,
+            const word& cloudName
+        );
+
         //- Construct from mesh and a list of particles
         Cloud
         (
@@ -138,12 +146,12 @@ public:
             const IDLList<ParticleType>& particles
         );
 
-        //- Construct from mesh by reading from file with given cloud instance
-        //  Optionally disable checking of class name for post-processing
+        //- Read construct from file(s) with given cloud instance.
         Cloud
         (
             const polyMesh& pMesh,
             const word& cloudName,
+            //! Disable checking of class name (eg, for post-processing)
             const bool checkClass = true
         );
 
@@ -153,7 +161,7 @@ public:
         // Access
 
             //- Return the polyMesh reference
-            const polyMesh& pMesh() const
+            const polyMesh& pMesh() const noexcept
             {
                 return polyMesh_;
             }
diff --git a/src/lagrangian/basic/Cloud/CloudIO.C b/src/lagrangian/basic/Cloud/CloudIO.C
index 42ceecd762..70f14cac28 100644
--- a/src/lagrangian/basic/Cloud/CloudIO.C
+++ b/src/lagrangian/basic/Cloud/CloudIO.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017, 2020 OpenFOAM Foundation
-    Copyright (C) 2017-2022 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -49,7 +49,7 @@ void Foam::Cloud<ParticleType>::readCloudUniformProperties()
         time().timeName(),
         "uniform"/cloud::prefix/name(),
         db(),
-        IOobject::MUST_READ_IF_MODIFIED,
+        IOobject::MUST_READ,
         IOobject::NO_WRITE,
         IOobject::NO_REGISTER
     );
@@ -104,6 +104,7 @@ void Foam::Cloud<ParticleType>::writeCloudUniformProperties() const
     labelList np(Pstream::nProcs(), Zero);
     np[Pstream::myProcNo()] = ParticleType::particleCount_;
 
+    // FIXME: replace with  Pstream::allGatherList(np);
     Pstream::listCombineReduce(np, maxEqOp<label>());
 
     uniformPropsDict.add
@@ -114,9 +115,8 @@ void Foam::Cloud<ParticleType>::writeCloudUniformProperties() const
 
     forAll(np, i)
     {
-        word procName("processor" + Foam::name(i));
-        uniformPropsDict.add(procName, dictionary());
-        uniformPropsDict.subDict(procName).add("particleCount", np[i]);
+        const word procName("processor" + Foam::name(i));
+        uniformPropsDict.subDictOrAdd(procName).add("particleCount", np[i]);
     }
 
     uniformPropsDict.writeObject
@@ -169,17 +169,8 @@ Foam::Cloud<ParticleType>::Cloud
     const bool checkClass
 )
 :
-    cloud(pMesh, cloudName),
-    polyMesh_(pMesh),
-    labels_(),
-    cellWallFacesPtr_(),
-    geometryType_(cloud::geometryType::COORDINATES)
+    Cloud<ParticleType>(pMesh, Foam::zero{}, cloudName)
 {
-    checkPatches();
-
-    (void)polyMesh_.tetBasePtIs();
-    (void)polyMesh_.oldCellCentres();
-
     initCloud(checkClass);
 }
 
diff --git a/src/lagrangian/basic/IOPosition/IOPosition.C b/src/lagrangian/basic/IOPosition/IOPosition.C
index ad772a278e..7630396cc6 100644
--- a/src/lagrangian/basic/IOPosition/IOPosition.C
+++ b/src/lagrangian/basic/IOPosition/IOPosition.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2017-2021 OpenCFD Ltd.
+    Copyright (C) 2017-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -72,18 +72,18 @@ bool Foam::IOPosition<CloudType>::writeData(Ostream& os) const
     {
         case cloud::geometryType::COORDINATES:
         {
-            forAllConstIters(cloud_, iter)
+            for (const auto& p : cloud_)
             {
-                iter().writeCoordinates(os);
+                p.writeCoordinates(os);
                 os  << nl;
             }
             break;
         }
         case cloud::geometryType::POSITIONS:
         {
-            forAllConstIters(cloud_, iter)
+            for (const auto& p : cloud_)
             {
-                iter().writePosition(os);
+                p.writePosition(os);
                 os  << nl;
             }
             break;
diff --git a/src/lagrangian/basic/IOPosition/IOPosition.H b/src/lagrangian/basic/IOPosition/IOPosition.H
index 0ffd43ea2f..9a8a2beb15 100644
--- a/src/lagrangian/basic/IOPosition/IOPosition.H
+++ b/src/lagrangian/basic/IOPosition/IOPosition.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef IOPosition_H
-#define IOPosition_H
+#ifndef Foam_IOPosition_H
+#define Foam_IOPosition_H
 
 #include "cloud.H"
 #include "regIOobject.H"
@@ -55,7 +55,7 @@ class IOPosition
 :
     public regIOobject
 {
-    // Private data
+    // Private Data
 
         cloud::geometryType geometryType_;
 
@@ -65,7 +65,7 @@ class IOPosition
 
 public:
 
-    // Static data
+    // Static Data
 
         //- Runtime type name information. Use cloud type.
         virtual const word& type() const
@@ -77,7 +77,7 @@ public:
     // Constructors
 
         //- Construct from cloud
-        IOPosition
+        explicit IOPosition
         (
             const CloudType& c,
             cloud::geometryType geomType = cloud::geometryType::COORDINATES
diff --git a/src/lagrangian/basic/indexedParticle/indexedParticleCloud.H b/src/lagrangian/basic/indexedParticle/indexedParticleCloud.H
index 7ecc16ec62..5c2993b472 100644
--- a/src/lagrangian/basic/indexedParticle/indexedParticleCloud.H
+++ b/src/lagrangian/basic/indexedParticle/indexedParticleCloud.H
@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef indexedParticleCloud_H
-#define indexedParticleCloud_H
+#ifndef Foam_indexedParticleCloud_H
+#define Foam_indexedParticleCloud_H
 
 #include "Cloud.H"
 #include "indexedParticle.H"
@@ -53,26 +53,38 @@ class indexedParticleCloud
 :
     public Cloud<indexedParticle>
 {
-    // Private Member Functions
-
-        //- No copy construct
-        indexedParticleCloud(const indexedParticleCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const indexedParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef indexedParticle parcelType;
+
+    //- No copy construct
+    indexedParticleCloud(const indexedParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const indexedParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit indexedParticleCloud
         (
             const polyMesh& mesh,
             const word& cloudName = cloud::defaultName,
             bool readFields = true
         );
+
+        //- Construct without particles
+        explicit indexedParticleCloud
+        (
+            const polyMesh& mesh,
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<indexedParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/src/lagrangian/basic/injectedParticle/injectedParticleCloud.C b/src/lagrangian/basic/injectedParticle/injectedParticleCloud.C
index c92cf67652..f04f2076fe 100644
--- a/src/lagrangian/basic/injectedParticle/injectedParticleCloud.C
+++ b/src/lagrangian/basic/injectedParticle/injectedParticleCloud.C
@@ -27,11 +27,14 @@ License
 
 #include "injectedParticleCloud.H"
 
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
 namespace Foam
 {
     defineNamedTemplateTypeNameAndDebug(Cloud<injectedParticle>, 0);
 }
 
+
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
 Foam::injectedParticleCloud::injectedParticleCloud
@@ -62,12 +65,6 @@ Foam::injectedParticleCloud::injectedParticleCloud
 {}
 
 
-// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
-
-Foam::injectedParticleCloud::~injectedParticleCloud()
-{}
-
-
 // * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
 
 void Foam::injectedParticleCloud::readObjects(const objectRegistry& obr)
diff --git a/src/lagrangian/basic/injectedParticle/injectedParticleCloud.H b/src/lagrangian/basic/injectedParticle/injectedParticleCloud.H
index dca1349e92..76b4f394d0 100644
--- a/src/lagrangian/basic/injectedParticle/injectedParticleCloud.H
+++ b/src/lagrangian/basic/injectedParticle/injectedParticleCloud.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef injectedParticleCloud_H
-#define injectedParticleCloud_H
+#ifndef Foam_injectedParticleCloud_H
+#define Foam_injectedParticleCloud_H
 
 #include "Cloud.H"
 #include "injectedParticle.H"
@@ -46,7 +46,6 @@ SourceFiles
 namespace Foam
 {
 
-
 /*---------------------------------------------------------------------------*\
                    Class injectedParticleCloud Declaration
 \*---------------------------------------------------------------------------*/
@@ -55,30 +54,39 @@ class injectedParticleCloud
 :
     public Cloud<injectedParticle>
 {
-
-private:
-
-    // Private Member Functions
-
-        //- No copy construct
-        injectedParticleCloud(const injectedParticleCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const injectedParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef injectedParticle parcelType;
+
+    //- No copy construct
+    injectedParticleCloud(const injectedParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const injectedParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct from mesh and cloud name
+        //- Read construct
         injectedParticleCloud
         (
             const polyMesh& mesh,
-            const word& name,
+            const word& cloudName,
             const bool readFields = true
         );
 
+        //- Construct without particles
+        injectedParticleCloud
+        (
+            const polyMesh& mesh,
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<injectedParticle>(mesh, Foam::zero{}, cloudName)
+        {}
+
         //- Copy constructor with new name
         injectedParticleCloud(const injectedParticleCloud& c, const word& name);
 
@@ -93,18 +101,16 @@ public:
 
 
     //- Destructor
-    virtual ~injectedParticleCloud();
+    virtual ~injectedParticleCloud() = default;
 
 
     // Member Functions
 
-        // I-O
+        //- Read particle fields as objects from the obr registry
+        virtual void readObjects(const objectRegistry& obr);
 
-            //- Read particle fields as objects from the obr registry
-            virtual void readObjects(const objectRegistry& obr);
-
-            //- Write particle fields as objects into the obr registry
-            virtual void writeObjects(objectRegistry& obr) const;
+        //- Write particle fields as objects into the obr registry
+        virtual void writeObjects(objectRegistry& obr) const;
 };
 
 
diff --git a/src/lagrangian/basic/passiveParticle/passiveParticleCloud.C b/src/lagrangian/basic/passiveParticle/passiveParticleCloud.C
index cd182042a9..df281d9d4a 100644
--- a/src/lagrangian/basic/passiveParticle/passiveParticleCloud.C
+++ b/src/lagrangian/basic/passiveParticle/passiveParticleCloud.C
@@ -52,15 +52,4 @@ Foam::passiveParticleCloud::passiveParticleCloud
 }
 
 
-Foam::passiveParticleCloud::passiveParticleCloud
-(
-    const polyMesh& mesh,
-    const word& cloudName,
-    const IDLList<passiveParticle>& particles
-)
-:
-    Cloud<passiveParticle>(mesh, cloudName, particles)
-{}
-
-
 // ************************************************************************* //
diff --git a/src/lagrangian/basic/passiveParticle/passiveParticleCloud.H b/src/lagrangian/basic/passiveParticle/passiveParticleCloud.H
index c34fb48c55..5ab14f09e0 100644
--- a/src/lagrangian/basic/passiveParticle/passiveParticleCloud.H
+++ b/src/lagrangian/basic/passiveParticle/passiveParticleCloud.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011 OpenFOAM Foundation
-    Copyright (C) 2019 OpenCFD Ltd.
+    Copyright (C) 2019-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef passiveParticleCloud_H
-#define passiveParticleCloud_H
+#ifndef Foam_passiveParticleCloud_H
+#define Foam_passiveParticleCloud_H
 
 #include "Cloud.H"
 #include "passiveParticle.H"
@@ -54,20 +54,21 @@ class passiveParticleCloud
 :
     public Cloud<passiveParticle>
 {
-    // Private Member Functions
-
-        //- No copy construct
-        passiveParticleCloud(const passiveParticleCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const passiveParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef passiveParticle parcelType;
+
+    //- No copy construct
+    passiveParticleCloud(const passiveParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const passiveParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit passiveParticleCloud
         (
             const polyMesh& mesh,
@@ -75,13 +76,16 @@ public:
             bool readFields = true
         );
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         passiveParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<passiveParticle>& particles
-        );
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<passiveParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/HeatTransferCoeff/HeatTransferCoeff.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/HeatTransferCoeff/HeatTransferCoeff.C
index 51ae1bc7be..28806d1f47 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/HeatTransferCoeff/HeatTransferCoeff.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/HeatTransferCoeff/HeatTransferCoeff.C
@@ -92,10 +92,8 @@ void Foam::HeatTransferCoeff<CloudType>::postEvolve
         const_cast<typename parcelType::trackingData&>(td);
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         scalar Ts, rhos, mus, Pr, kappas;
         p.template calcSurfaceValues<CloudType>
         (
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicReynoldsNumber/KinematicReynoldsNumber.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicReynoldsNumber/KinematicReynoldsNumber.C
index 5193283ecf..289c50665b 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicReynoldsNumber/KinematicReynoldsNumber.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicReynoldsNumber/KinematicReynoldsNumber.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021-2022 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -85,10 +85,8 @@ void Foam::KinematicReynoldsNumber<CloudType>::postEvolve
     Re.resize(c.size());
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         Re[parceli++] = p.Re(td);
     }
 
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicWeberNumber/KinematicWeberNumber.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicWeberNumber/KinematicWeberNumber.C
index 2c067d6923..8b2bef3891 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicWeberNumber/KinematicWeberNumber.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/KinematicWeberNumber/KinematicWeberNumber.C
@@ -87,10 +87,8 @@ void Foam::KinematicWeberNumber<CloudType>::postEvolve
     We.resize(c.size());
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         We[parceli++] = p.We(td, sigma_);
     }
 
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/NusseltNumber/NusseltNumber.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/NusseltNumber/NusseltNumber.C
index d2d785a10a..2b33c343ee 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/NusseltNumber/NusseltNumber.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/NusseltNumber/NusseltNumber.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021-2022 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -92,10 +92,8 @@ void Foam::NusseltNumber<CloudType>::postEvolve
         const_cast<typename parcelType::trackingData&>(td);
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         scalar Ts, rhos, mus, Pr, kappas;
         p.template calcSurfaceValues<CloudType>
         (
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleDose/ParticleDose.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleDose/ParticleDose.C
index 02bfd9f97c..bde501e7b7 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleDose/ParticleDose.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ParticleDose/ParticleDose.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2022 OpenCFD Ltd.
+    Copyright (C) 2022-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -92,10 +92,8 @@ void Foam::ParticleDose<CloudType>::postEvolve
     const auto& G = mesh.lookupObject<volScalarField>(GName_);
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         D[parceli] += G[p.cell()]*mesh.time().deltaTValue();
         parceli++;
     }
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ReactingWeberNumber/ReactingWeberNumber.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ReactingWeberNumber/ReactingWeberNumber.C
index de6821d6c0..1d23e2033d 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ReactingWeberNumber/ReactingWeberNumber.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ReactingWeberNumber/ReactingWeberNumber.C
@@ -93,10 +93,8 @@ void Foam::ReactingWeberNumber<CloudType>::postEvolve
     const auto& rhoInterp = td.rhoInterp();
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         const auto& coords = p.coordinates();
         const auto& tetIs = p.currentTetIndices();
 
diff --git a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ThermoReynoldsNumber/ThermoReynoldsNumber.C b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ThermoReynoldsNumber/ThermoReynoldsNumber.C
index 090f37d518..ca786fea25 100644
--- a/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ThermoReynoldsNumber/ThermoReynoldsNumber.C
+++ b/src/lagrangian/intermediate/submodels/CloudFunctionObjects/ThermoReynoldsNumber/ThermoReynoldsNumber.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021-2022 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -89,10 +89,8 @@ void Foam::ThermoReynoldsNumber<CloudType>::postEvolve
         const_cast<typename parcelType::trackingData&>(td);
 
     label parceli = 0;
-    forAllConstIters(c, parcelIter)
+    for (const parcelType& p : c)
     {
-        const parcelType& p = parcelIter();
-
         scalar Ts, rhos, mus, Pr, kappas;
         p.template calcSurfaceValues<CloudType>
         (
diff --git a/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloud.H b/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloud.H
index 1827a33def..5873fd098a 100644
--- a/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloud.H
+++ b/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloud.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef moleculeCloud_H
-#define moleculeCloud_H
+#ifndef Foam_moleculeCloud_H
+#define Foam_moleculeCloud_H
 
 #include "Cloud.H"
 #include "molecule.H"
@@ -133,18 +133,22 @@ class moleculeCloud
             const molecule::constantProperties& cP
         );
 
-        //- No copy construct
-        moleculeCloud(const moleculeCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const moleculeCloud&) = delete;
-
 
 public:
 
+    //- Type of parcel within the cloud
+    typedef molecule parcelType;
+
+    //- No copy construct
+    moleculeCloud(const moleculeCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const moleculeCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh and potential references
+        //- Read construct given mesh and potential references
         moleculeCloud
         (
             const polyMesh& mesh,
@@ -152,7 +156,7 @@ public:
             bool readFields = true
         );
 
-        //- Construct given mesh, potential and mdInitialiseDict
+        //- Read construct given mesh, potential and mdInitialiseDict
         moleculeCloud
         (
             const polyMesh& mesh,
@@ -178,19 +182,32 @@ public:
 
     // Access
 
-        inline const polyMesh& mesh() const;
+        // Same as pMesh()
+        const polyMesh& mesh() const noexcept { return mesh_; }
 
-        inline const potential& pot() const;
+        const potential& pot() const { return pot_; }
 
-        inline const List<DynamicList<molecule*>>& cellOccupancy() const;
+        const List<DynamicList<molecule*>>& cellOccupancy() const
+        {
+            return cellOccupancy_;
+        }
 
-        inline const InteractionLists<molecule>& il() const;
+        const InteractionLists<molecule>& il() const
+        {
+            return il_;
+        }
 
-        inline const List<molecule::constantProperties> constProps() const;
+        const List<molecule::constantProperties>& constProps() const
+        {
+            return constPropList_;
+        }
 
-        inline const molecule::constantProperties& constProps(label id) const;
+        const molecule::constantProperties& constProps(label id) const
+        {
+            return constPropList_[id];
+        }
 
-        inline Random& rndGen();
+        Random& rndGen() { return rndGen_; }
 
 
     // Member Operators
diff --git a/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloudI.H b/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloudI.H
index b109b9ad29..398b02dae0 100644
--- a/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloudI.H
+++ b/src/lagrangian/molecularDynamics/molecule/moleculeCloud/moleculeCloudI.H
@@ -338,52 +338,4 @@ inline Foam::vector Foam::moleculeCloud::equipartitionAngularMomentum
 }
 
 
-// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
-
-inline const Foam::polyMesh& Foam::moleculeCloud::mesh() const
-{
-    return mesh_;
-}
-
-
-inline const Foam::potential& Foam::moleculeCloud::pot() const
-{
-    return pot_;
-}
-
-
-inline const Foam::List<Foam::DynamicList<Foam::molecule*>>&
-    Foam::moleculeCloud::cellOccupancy() const
-{
-    return cellOccupancy_;
-}
-
-
-inline const Foam::InteractionLists<Foam::molecule>&
-    Foam::moleculeCloud::il() const
-{
-    return il_;
-}
-
-
-inline const Foam::List<Foam::molecule::constantProperties>
-    Foam::moleculeCloud::constProps() const
-{
-    return constPropList_;
-}
-
-
-inline const Foam::molecule::constantProperties&
-    Foam::moleculeCloud::constProps(label id) const
-{
-    return constPropList_[id];
-}
-
-
-inline Foam::Random& Foam::moleculeCloud::rndGen()
-{
-    return rndGen_;
-}
-
-
 // ************************************************************************* //
diff --git a/src/lagrangian/solidParticle/solidParticleCloud.H b/src/lagrangian/solidParticle/solidParticleCloud.H
index eced0ea51d..81c833d095 100644
--- a/src/lagrangian/solidParticle/solidParticleCloud.H
+++ b/src/lagrangian/solidParticle/solidParticleCloud.H
@@ -31,14 +31,13 @@ Description
     A Cloud of solid particles
 
 SourceFiles
-    solidParticleCloudI.H
     solidParticleCloud.C
     solidParticleCloudIO.C
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef solidParticleCloud_H
-#define solidParticleCloud_H
+#ifndef Foam_solidParticleCloud_H
+#define Foam_solidParticleCloud_H
 
 #include "Cloud.H"
 #include "solidParticle.H"
@@ -60,7 +59,7 @@ class solidParticleCloud
 :
     public Cloud<solidParticle>
 {
-    // Private data
+    // Private Data
 
         const fvMesh& mesh_;
 
@@ -71,20 +70,21 @@ class solidParticleCloud
         scalar mu_;
 
 
-    // Private Member Functions
-
-        //- No copy construct
-        solidParticleCloud(const solidParticleCloud&) = delete;
-
-        //- No copy assignment
-        void operator=(const solidParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef solidParticle parcelType;
+
+    //- No copy construct
+    solidParticleCloud(const solidParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const solidParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit solidParticleCloud
         (
             const fvMesh& mesh,
@@ -95,20 +95,20 @@ public:
 
     // Member Functions
 
-        // Access
+    // Access
 
-            inline const fvMesh& mesh() const;
+        const fvMesh& mesh() const { return mesh_; }
 
-            inline scalar rhop() const;
-            inline scalar e() const;
-            inline scalar mu() const;
+        scalar rhop() const noexcept { return rhop_; }
+        scalar e() const noexcept { return e_; }
+        scalar mu() const noexcept { return mu_; }
 
 
-        // Edit
+    // Edit
 
-            //- Move the particles under the influence of the given
-            //  gravitational acceleration
-            void move(const dimensionedVector& g);
+        //- Move the particles under the influence of the given
+        //-  gravitational acceleration
+        void move(const dimensionedVector& g);
 };
 
 
@@ -118,10 +118,6 @@ public:
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
-#include "solidParticleCloudI.H"
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
 #endif
 
 // ************************************************************************* //
diff --git a/src/lagrangian/solidParticle/solidParticleCloudI.H b/src/lagrangian/solidParticle/solidParticleCloudI.H
index ed4dd0fa72..7cec1b4541 100644
--- a/src/lagrangian/solidParticle/solidParticleCloudI.H
+++ b/src/lagrangian/solidParticle/solidParticleCloudI.H
@@ -1,53 +1 @@
-/*---------------------------------------------------------------------------*\
-  =========                 |
-  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
-   \\    /   O peration     |
-    \\  /    A nd           | www.openfoam.com
-     \\/     M anipulation  |
--------------------------------------------------------------------------------
-    Copyright (C) 2011 OpenFOAM Foundation
--------------------------------------------------------------------------------
-License
-    This file is part of OpenFOAM.
-
-    OpenFOAM is free software: you can redistribute it and/or modify it
-    under the terms of the GNU General Public License as published by
-    the Free Software Foundation, either version 3 of the License, or
-    (at your option) any later version.
-
-    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
-    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
-    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
-    for more details.
-
-    You should have received a copy of the GNU General Public License
-    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.
-
-\*---------------------------------------------------------------------------*/
-
-// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
-
-inline const Foam::fvMesh& Foam::solidParticleCloud::mesh() const
-{
-    return mesh_;
-}
-
-
-inline Foam::scalar Foam::solidParticleCloud::rhop() const
-{
-    return rhop_;
-}
-
-
-inline Foam::scalar Foam::solidParticleCloud::e() const
-{
-    return e_;
-}
-
-
-inline Foam::scalar Foam::solidParticleCloud::mu() const
-{
-    return mu_;
-}
-
-// ************************************************************************* //
+#warning File removed - left for old dependency check only
diff --git a/src/mesh/snappyHexMesh/meshRefinement/meshRefinementRefine.C b/src/mesh/snappyHexMesh/meshRefinement/meshRefinementRefine.C
index 4d55996564..cec01d92c7 100644
--- a/src/mesh/snappyHexMesh/meshRefinement/meshRefinementRefine.C
+++ b/src/mesh/snappyHexMesh/meshRefinement/meshRefinementRefine.C
@@ -337,8 +337,8 @@ void Foam::meshRefinement::markFeatureCellLevel
     Cloud<trackedParticle> startPointCloud
     (
         mesh_,
-        "startPointCloud",
-        IDLList<trackedParticle>()
+        Foam::zero{},
+        "startPointCloud"
     );
 
 
@@ -492,12 +492,8 @@ void Foam::meshRefinement::markFeatureCellLevel
     }
 
 
-    Cloud<trackedParticle> cloud
-    (
-        mesh_,
-        "featureCloud",
-        IDLList<trackedParticle>()
-    );
+    // Start with empty cloud
+    Cloud<trackedParticle> cloud(mesh_, Foam::zero{}, "featureCloud");
 
     if (debug&meshRefinement::FEATURESEEDS)
     {
diff --git a/src/parallel/decompose/decompose/lagrangianFieldDecomposer.C b/src/parallel/decompose/decompose/lagrangianFieldDecomposer.C
index e89807d07c..46f3598d67 100644
--- a/src/parallel/decompose/decompose/lagrangianFieldDecomposer.C
+++ b/src/parallel/decompose/decompose/lagrangianFieldDecomposer.C
@@ -44,7 +44,7 @@ Foam::lagrangianFieldDecomposer::lagrangianFieldDecomposer
 )
 :
     procMesh_(procMesh),
-    positions_(procMesh, cloudName, IDLList<passiveParticle>()),
+    positions_(procMesh, Foam::zero{}, cloudName),  // Empty cloud
     particleIndices_(lagrangianPositions.size())
 {
     label pi = 0;
diff --git a/src/parallel/reconstruct/reconstruct/lagrangianReconstructor.C b/src/parallel/reconstruct/reconstruct/lagrangianReconstructor.C
index c2656072b7..508110e840 100644
--- a/src/parallel/reconstruct/reconstruct/lagrangianReconstructor.C
+++ b/src/parallel/reconstruct/reconstruct/lagrangianReconstructor.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2017 OpenFOAM Foundation
-    Copyright (C) 2018-2022 OpenCFD Ltd.
+    Copyright (C) 2018-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -58,11 +58,12 @@ Foam::label Foam::lagrangianReconstructor::reconstructPositions
     const word& cloudName
 ) const
 {
+    // Start with empty cloud
     passivePositionParticleCloud lagrangianPositions
     (
         mesh_,
-        cloudName,
-        IDLList<passivePositionParticle>()
+        Foam::zero{},
+        cloudName
     );
 
     forAll(procMeshes_, meshi)
@@ -78,10 +79,8 @@ Foam::label Foam::lagrangianReconstructor::reconstructPositions
         // - written in the old format
         passivePositionParticleCloud lpi(procMeshes_[meshi], cloudName, false);
 
-        forAllConstIters(lpi, iter)
+        for (const passivePositionParticle& ppi : lpi)
         {
-            const passivePositionParticle& ppi = *iter;
-
             const label mappedCell =
             (
                 (ppi.cell() >= 0)
diff --git a/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.C b/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.C
index 4f714ad287..895b18ae3c 100644
--- a/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.C
+++ b/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.C
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -52,15 +52,4 @@ Foam::passivePositionParticleCloud::passivePositionParticleCloud
 }
 
 
-Foam::passivePositionParticleCloud::passivePositionParticleCloud
-(
-    const polyMesh& mesh,
-    const word& cloudName,
-    const IDLList<passivePositionParticle>& particles
-)
-:
-    Cloud<passivePositionParticle>(mesh, cloudName, particles)
-{}
-
-
 // ************************************************************************* //
diff --git a/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.H b/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.H
index dab774fcfc..a864a15c3a 100644
--- a/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.H
+++ b/src/parallel/reconstruct/reconstruct/passivePositionParticleCloud.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2021 OpenCFD Ltd.
+    Copyright (C) 2021-2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -34,8 +34,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef passivePositionParticleCloud_H
-#define passivePositionParticleCloud_H
+#ifndef Foam_passivePositionParticleCloud_H
+#define Foam_passivePositionParticleCloud_H
 
 #include "Cloud.H"
 #include "passivePositionParticle.H"
@@ -53,21 +53,21 @@ class passivePositionParticleCloud
 :
     public Cloud<passivePositionParticle>
 {
-    // Private Member Functions
-
-        //- No copy construct
-        passivePositionParticleCloud(const passivePositionParticleCloud&) =
-            delete;
-
-        //- No copy assignment
-        void operator=(const passivePositionParticleCloud&) = delete;
-
-
 public:
 
+    //- Type of parcel within the cloud
+    typedef passivePositionParticle parcelType;
+
+    //- No copy construct
+    passivePositionParticleCloud(const passivePositionParticleCloud&) = delete;
+
+    //- No copy assignment
+    void operator=(const passivePositionParticleCloud&) = delete;
+
+
     // Constructors
 
-        //- Construct given mesh
+        //- Read construct
         explicit passivePositionParticleCloud
         (
             const polyMesh& mesh,
@@ -75,13 +75,16 @@ public:
             bool readFields = true
         );
 
-        //- Construct from mesh, cloud name, and a list of particles
+        //- Construct without particles
         passivePositionParticleCloud
         (
             const polyMesh& mesh,
-            const word& cloudName,
-            const IDLList<passivePositionParticle>& particles
-        );
+            const Foam::zero,
+            const word& cloudName = cloud::defaultName
+        )
+        :
+            Cloud<passivePositionParticle>(mesh, Foam::zero{}, cloudName)
+        {}
 };
 
 
diff --git a/src/surfMesh/surfaceRegistry/surfaceRegistry.C b/src/surfMesh/surfaceRegistry/surfaceRegistry.C
index 49c38628b2..67cbb9ea49 100644
--- a/src/surfMesh/surfaceRegistry/surfaceRegistry.C
+++ b/src/surfMesh/surfaceRegistry/surfaceRegistry.C
@@ -42,6 +42,15 @@ Foam::word Foam::surfaceRegistry::defaultName("default");
 
 // * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
 
+Foam::surfaceRegistry::surfaceRegistry
+(
+    const objectRegistry& obr
+)
+:
+    surfaceRegistry(obr, surfaceRegistry::defaultName)
+{}
+
+
 Foam::surfaceRegistry::surfaceRegistry
 (
     const objectRegistry& obr,
@@ -52,12 +61,13 @@ Foam::surfaceRegistry::surfaceRegistry
     (
         IOobject
         (
-            (surfName.size() ? surfName : defaultName),
+            (surfName.empty() ? surfaceRegistry::defaultName : surfName),
             obr.time().timeName(),
-            prefix,
+            surfaceRegistry::prefix,
             obr,
             IOobjectOption::NO_READ,
-            IOobjectOption::NO_WRITE
+            IOobjectOption::NO_WRITE,
+            IOobjectOption::REGISTER
         )
     )
 {}
diff --git a/src/surfMesh/surfaceRegistry/surfaceRegistry.H b/src/surfMesh/surfaceRegistry/surfaceRegistry.H
index 6af8495764..124bd74824 100644
--- a/src/surfMesh/surfaceRegistry/surfaceRegistry.H
+++ b/src/surfMesh/surfaceRegistry/surfaceRegistry.H
@@ -35,8 +35,8 @@ SourceFiles
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef surfaceRegistry_H
-#define surfaceRegistry_H
+#ifndef Foam_surfaceRegistry_H
+#define Foam_surfaceRegistry_H
 
 #include "objectRegistry.H"
 
@@ -53,20 +53,9 @@ class surfaceRegistry
 :
     public objectRegistry
 {
-
-    // Private Member Functions
-
-        //- No copy construct
-        surfaceRegistry(const surfaceRegistry&) = delete;
-
-        //- No copy assignment
-        surfaceRegistry& operator=(const surfaceRegistry&) = delete;
-
-
 public:
 
-    //- Runtime type information
-    TypeName("surfaceRegistry");
+    // Static Data Members
 
         //- The prefix to local: %surfaces
         static const word prefix;
@@ -75,19 +64,30 @@ public:
         static word defaultName;
 
 
+    //- Runtime type information
+    TypeName("surfaceRegistry");
+
+
+    // Generated Methods
+
+        //- No copy construct
+        surfaceRegistry(const surfaceRegistry&) = delete;
+
+        //- No copy assignment
+        surfaceRegistry& operator=(const surfaceRegistry&) = delete;
+
+
     // Constructors
 
-        //- Construct for the given objectRegistry and named surface
-        surfaceRegistry
-        (
-            const objectRegistry& obr,
-            const word& surfName = word::null
-        );
+        //- Construct for given objectRegistry. Uses default surface name
+        explicit surfaceRegistry(const objectRegistry& obr);
+
+        //- Construct for given objectRegistry and named surface
+        surfaceRegistry(const objectRegistry& obr, const word& surfName);
 
 
     //- Destructor
     virtual ~surfaceRegistry() = default;
-
 };