diff --git a/etc/config.sh/bash_completion b/etc/config.sh/bash_completion
index 9a748badde..8134ad7204 100644
--- a/etc/config.sh/bash_completion
+++ b/etc/config.sh/bash_completion
@@ -5,7 +5,7 @@
 #   \\  /    A nd           | www.openfoam.com
 #    \\/     M anipulation  |
 #------------------------------------------------------------------------------
-#     Copyright (C) 2017-2022 OpenCFD Ltd.
+#     Copyright (C) 2017-2023 OpenCFD Ltd.
 #------------------------------------------------------------------------------
 # License
 #     This file is part of OpenFOAM, distributed under GPL-3.0-or-later.
@@ -146,7 +146,7 @@ _of_complete_()
         COMPREPLY=($(compgen -W "$choices" -- ${cur}))
         ;;
     -fileHandler)
-        choices="collated uncollated hostCollated masterUncollated"
+        choices="collated uncollated hostCollated hostUncollated masterUncollated"
         COMPREPLY=($(compgen -W "$choices" -- ${cur}))
         ;;
     *)
diff --git a/src/OpenFOAM/Make/files b/src/OpenFOAM/Make/files
index cb0be37821..0edb074fde 100644
--- a/src/OpenFOAM/Make/files
+++ b/src/OpenFOAM/Make/files
@@ -21,7 +21,7 @@ $(fileOps)/fileOperation/fileOperation.C
 $(fileOps)/fileOperation/fileOperationBroadcast.C
 $(fileOps)/fileOperation/fileOperationNew.C
 $(fileOps)/fileOperation/fileOperationRanks.C
-$(fileOps)/fileOperationInitialise/fileOperationInitialise.C
+$(fileOps)/fileOperation/fileOperationInitialise.C
 $(fileOps)/dummyFileOperation/dummyFileOperation.C
 $(fileOps)/uncollatedFileOperation/uncollatedFileOperation.C
 $(fileOps)/masterUncollatedFileOperation/masterUncollatedFileOperation.C
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
index 1c846ae5d8..2318c474d7 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.C
@@ -68,11 +68,11 @@ namespace fileOperations
         collatedFileOperation::maxThreadFileBufferSize
     );
 
-    // Mark as needing threaded mpi
+    // Threaded MPI: depending on buffering
     addNamedToRunTimeSelectionTable
     (
         fileOperationInitialise,
-        collatedFileOperationInitialise,
+        fileOperationInitialise_collated,
         word,
         collated
     );
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
index 92ce70c71a..04acd2ae0f 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/collatedFileOperation.H
@@ -50,6 +50,7 @@ SourceFiles
 #define Foam_fileOperations_collatedFileOperation_H
 
 #include "masterUncollatedFileOperation.H"
+#include "fileOperationInitialise.H"
 #include "OFstreamCollator.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
@@ -173,32 +174,33 @@ public:
 
 
 /*---------------------------------------------------------------------------*\
-               Class collatedFileOperationInitialise Declaration
+               Class fileOperationInitialise_collated Declaration
 \*---------------------------------------------------------------------------*/
 
-//! Internal class only
-class collatedFileOperationInitialise
+//- A fileOperation initialiser for collated file handlers.
+//- Requires threading for non-zero maxThreadFileBufferSize.
+class fileOperationInitialise_collated
 :
-    public masterUncollatedFileOperationInitialise
+    public fileOperationInitialise
 {
 public:
 
     // Constructors
 
         //- Construct from components
-        collatedFileOperationInitialise(int& argc, char**& argv)
+        fileOperationInitialise_collated(int& argc, char**& argv)
         :
-            masterUncollatedFileOperationInitialise(argc, argv)
+            fileOperationInitialise(argc, argv)
         {}
 
 
     //- Destructor
-    virtual ~collatedFileOperationInitialise() = default;
+    virtual ~fileOperationInitialise_collated() = default;
 
 
     // Member Functions
 
-        //- Requires threading for non-zero maxThreadFileBufferSize
+        //- The (MPI) threading requirement depends on buffering
         virtual bool needsThreading() const
         {
             return (collatedFileOperation::maxThreadFileBufferSize > 0);
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.C
index f7ede70f30..8ee087e691 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.C
@@ -49,12 +49,11 @@ namespace fileOperations
         comm
     );
 
-    // Register initialisation routine. Signals need for threaded mpi and
-    // handles command line arguments
+    // Threaded MPI: depending on buffering
     addNamedToRunTimeSelectionTable
     (
         fileOperationInitialise,
-        hostCollatedFileOperationInitialise,
+        fileOperationInitialise_collated,
         word,
         hostCollated
     );
diff --git a/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.H
index 23840308c8..25ab873fc0 100644
--- a/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/collatedFileOperation/hostCollatedFileOperation.H
@@ -129,31 +129,6 @@ public:
 };
 
 
-/*---------------------------------------------------------------------------*\
-            Class hostCollatedFileOperationInitialise Declaration
-\*---------------------------------------------------------------------------*/
-
-//! Internal class only
-class hostCollatedFileOperationInitialise
-:
-    public collatedFileOperationInitialise
-{
-public:
-
-    // Constructors
-
-        //- Construct from components
-        hostCollatedFileOperationInitialise(int& argc, char**& argv)
-        :
-            collatedFileOperationInitialise(argc, argv)
-        {}
-
-
-    //- Destructor
-    virtual ~hostCollatedFileOperationInitialise() = default;
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace fileOperations
diff --git a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.C b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.C
similarity index 78%
rename from src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.C
rename to src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.C
index f934b4bd22..978e4a9d09 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.C
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.C
@@ -50,37 +50,44 @@ Foam::fileOperations::fileOperationInitialise::fileOperationInitialise
     char**& argv
 )
 {
-    // Check for -ioRanks, which requires an argument
+    // Check for -ioRanks: requires an argument
     int index = -1;
     for (int argi = 1; argi < argc; ++argi)
     {
-        if (argv[argi][0] == '-')
+        const char *optName = argv[argi];
+
+        if (optName[0] == '-')
         {
-            const char *optName = &argv[argi][1];
+            ++optName;  // Looks like an option, skip leading '-'
+            bool emitErrorMessage = false;
 
             if (strcmp(optName, "ioRanks") == 0)
             {
+                // Requires a parameter
                 if (argi < argc-1)
                 {
                     index = argi;
-                    Foam::setEnv("FOAM_IORANKS", argv[argi+1], true);
+                    ++argi;
+                    Foam::setEnv("FOAM_IORANKS", argv[argi], true);
                     break;
                 }
                 else
                 {
-                    // No argument to -ioRanks.
-                    // Give error message as in argList.
-                    // Slight problem: Pstream not yet initialised so
-                    // - no master-only output
-                    // - no early exit
-
-                    Info<< nl
-                        << "Error: option '-ioRanks' requires a list of"
-                           " IO ranks as argument" << nl << nl;
-
-                    //UPstream::exit(1);  // works for serial and parallel
+                    emitErrorMessage = true;
                 }
             }
+
+            if (emitErrorMessage)
+            {
+                // Missing argument: emit message but not exit or
+                // FatalError since Pstream etc are not yet initialised
+
+                Info<< nl
+                    << "Error: option '-" << optName
+                    << "' requires an argument" << nl << nl;
+
+                //NO: UPstream::exit(1);  // works for serial and parallel
+            }
         }
     }
 
diff --git a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.H b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.H
similarity index 74%
rename from src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.H
rename to src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.H
index a5f6d91fe6..ebd129b3d1 100644
--- a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/fileOperationInitialise.H
+++ b/src/OpenFOAM/global/fileOperations/fileOperation/fileOperationInitialise.H
@@ -6,6 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017-2018 OpenFOAM Foundation
+    Copyright (C) 2023 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -33,8 +34,8 @@ Description
 
 \*---------------------------------------------------------------------------*/
 
-#ifndef fileOperationInitialise_H
-#define fileOperationInitialise_H
+#ifndef Foam_fileOperations_fileOperationInitialise_H
+#define Foam_fileOperations_fileOperationInitialise_H
 
 #include "runTimeSelectionTables.H"
 
@@ -79,7 +80,7 @@ public:
 
     // Selectors
 
-        //- Select type
+        //- Select initialisation type
         static autoPtr<fileOperationInitialise> New
         (
             const word& type, int& argc, char**& argv
@@ -92,11 +93,42 @@ public:
 
     // Member Functions
 
-        //- Threading required?
+        //- Requires (MPI) threading?
         virtual bool needsThreading() const = 0;
 };
 
 
+/*---------------------------------------------------------------------------*\
+              Class fileOperationInitialise_unthreaded Declaration
+\*---------------------------------------------------------------------------*/
+
+//- A fileOperation initialiser for unthreaded file handlers.
+class fileOperationInitialise_unthreaded
+:
+    public fileOperationInitialise
+{
+public:
+
+    // Constructors
+
+        //- Construct from components
+        fileOperationInitialise_unthreaded(int& argc, char**& argv)
+        :
+            fileOperationInitialise(argc, argv)
+        {}
+
+
+    //- Destructor
+    virtual ~fileOperationInitialise_unthreaded() = default;
+
+
+    // Member Functions
+
+        //- No (MPI) threading required
+        virtual bool needsThreading() const { return false; }
+};
+
+
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace fileOperations
diff --git a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/unthreadedInitialise.H b/src/OpenFOAM/global/fileOperations/fileOperationInitialise/unthreadedInitialise.H
deleted file mode 100644
index 36baf2b8cf..0000000000
--- a/src/OpenFOAM/global/fileOperations/fileOperationInitialise/unthreadedInitialise.H
+++ /dev/null
@@ -1,88 +0,0 @@
-/*---------------------------------------------------------------------------*\
-  =========                 |
-  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
-   \\    /   O peration     |
-    \\  /    A nd           | www.openfoam.com
-     \\/     M anipulation  |
--------------------------------------------------------------------------------
-    Copyright (C) 2017-2018 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/>.
-
-Class
-    Foam::unthreadedInitialise
-
-Description
-    A fileOperation initialiser for unthreaded file handlers
-
-\*---------------------------------------------------------------------------*/
-
-#ifndef unthreadedInitialise_H
-#define unthreadedInitialise_H
-
-#include "fileOperationInitialise.H"
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-namespace Foam
-{
-namespace fileOperations
-{
-
-/*---------------------------------------------------------------------------*\
-                     Class unthreadedInitialise Declaration
-\*---------------------------------------------------------------------------*/
-
-class unthreadedInitialise
-:
-    public fileOperationInitialise
-{
-public:
-
-    // Constructors
-
-        //- Construct from components
-        unthreadedInitialise(int& argc, char**& argv)
-        :
-            fileOperationInitialise(argc, argv)
-        {}
-
-
-    //- Destructor
-    virtual ~unthreadedInitialise() = default;
-
-
-    // Member Functions
-
-        //- No threading required
-        virtual bool needsThreading() const
-        {
-            return false;
-        }
-};
-
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-} // End namespace fileOperations
-} // End namespace Foam
-
-// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
-
-#endif
-
-// ************************************************************************* //
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index 700b44aa8c..7db6427ffa 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -27,6 +27,7 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "masterUncollatedFileOperation.H"
+#include "fileOperationInitialise.H"
 #include "addToRunTimeSelectionTable.H"
 #include "Pstream.H"
 #include "Time.H"
@@ -38,7 +39,6 @@ License
 #include "registerSwitch.H"
 #include "dummyISstream.H"
 #include "SubList.H"
-#include "unthreadedInitialise.H"
 
 /* * * * * * * * * * * * * * * Static Member Data  * * * * * * * * * * * * * */
 
@@ -71,11 +71,11 @@ namespace fileOperations
         masterUncollatedFileOperation::maxMasterFileBufferSize
     );
 
-    // Mark as not needing threaded mpi
+    // Threaded MPI: not required
     addNamedToRunTimeSelectionTable
     (
         fileOperationInitialise,
-        masterUncollatedFileOperationInitialise,
+        fileOperationInitialise_unthreaded,
         word,
         masterUncollated
     );
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
index bd908cb8de..b705312b4f 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
@@ -66,8 +66,6 @@ Description
 #include "OSspecific.H"
 #include "HashPtrTable.H"
 #include "DynamicList.H"
-#include "List.H"
-#include "unthreadedInitialise.H"
 
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
@@ -787,31 +785,6 @@ public:
 };
 
 
-/*---------------------------------------------------------------------------*\
-           Class masterUncollatedFileOperationInitialise Declaration
-\*---------------------------------------------------------------------------*/
-
-//! Internal class only
-class masterUncollatedFileOperationInitialise
-:
-    public unthreadedInitialise
-{
-public:
-
-    // Constructors
-
-        //- Construct from components
-        masterUncollatedFileOperationInitialise(int& argc, char**& argv)
-        :
-            unthreadedInitialise(argc, argv)
-        {}
-
-
-    //- Destructor
-    virtual ~masterUncollatedFileOperationInitialise() = default;
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace fileOperations
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.C
index ab7b28b175..e1541444bd 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.C
@@ -26,6 +26,7 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "hostUncollatedFileOperation.H"
+#include "fileOperationInitialise.H"
 #include "addToRunTimeSelectionTable.H"
 
 /* * * * * * * * * * * * * * * Static Member Data  * * * * * * * * * * * * * */
@@ -48,12 +49,11 @@ namespace fileOperations
         comm
     );
 
-    // Register initialisation routine. Signals need for threaded mpi and
-    // handles command line arguments
+    // Threaded MPI: not required
     addNamedToRunTimeSelectionTable
     (
         fileOperationInitialise,
-        hostUncollatedFileOperationInitialise,
+        fileOperationInitialise_unthreaded,
         word,
         hostUncollated
     );
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.H
index 6364eb853f..70b4f8949e 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/hostUncollatedFileOperation.H
@@ -94,31 +94,6 @@ public:
 };
 
 
-/*---------------------------------------------------------------------------*\
-            Class hostUncollatedFileOperationInitialise Declaration
-\*---------------------------------------------------------------------------*/
-
-//! Internal class only
-class hostUncollatedFileOperationInitialise
-:
-    public masterUncollatedFileOperationInitialise
-{
-public:
-
-    // Constructors
-
-        //- Construct from components
-        hostUncollatedFileOperationInitialise(int& argc, char**& argv)
-        :
-            masterUncollatedFileOperationInitialise(argc, argv)
-        {}
-
-
-    //- Destructor
-    virtual ~hostUncollatedFileOperationInitialise() = default;
-};
-
-
 // * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
 } // End namespace fileOperations
diff --git a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
index 9f2420e453..01103eecee 100644
--- a/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/uncollatedFileOperation/uncollatedFileOperation.C
@@ -27,12 +27,12 @@ License
 \*---------------------------------------------------------------------------*/
 
 #include "uncollatedFileOperation.H"
+#include "fileOperationInitialise.H"
 #include "Time.H"
 #include "Fstream.H"
 #include "addToRunTimeSelectionTable.H"
 #include "decomposedBlockData.H"
 #include "dummyISstream.H"
-#include "unthreadedInitialise.H"
 
 /* * * * * * * * * * * * * * * Static Member Data  * * * * * * * * * * * * * */
 
@@ -54,11 +54,11 @@ namespace fileOperations
         comm
     );
 
-    // Mark as not needing threaded mpi
+    // Threaded MPI: not required
     addNamedToRunTimeSelectionTable
     (
         fileOperationInitialise,
-        unthreadedInitialise,
+        fileOperationInitialise_unthreaded,
         word,
         uncollated
     );