diff --git a/applications/test/UIndirectList/Test-UIndirectList.C b/applications/test/UIndirectList/Test-UIndirectList.C
index 9dbd0e8b0e..a9d9cabd76 100644
--- a/applications/test/UIndirectList/Test-UIndirectList.C
+++ b/applications/test/UIndirectList/Test-UIndirectList.C
@@ -62,7 +62,9 @@ void testFind(const T& val, const ListType& lst)
 
 int main(int argc, char *argv[])
 {
-    List<label> completeList(20);
+    labelList completeList(20);
+    labelList scratch(20);
+    scratch = -1;
 
     forAll(completeList, i)
     {
@@ -71,12 +73,24 @@ int main(int argc, char *argv[])
 
     Info<< "raw : " << flatOutput(completeList) << nl << endl;
 
-    List<label> addresses{1, 0, 3, 7, 4, 8, 5, 1, 0, 3, 7, 4, 8, 5, };
+    List<label> addresses({ 1, 0, 3, 7, 4, 8, 5, 1, 0, 3, 7, 4, 8, 5 });
 
     labelUIndList idl1(completeList, addresses);
 
     printInfo(idl1);
 
+    labelList::subList slice(scratch, idl1.size());
+    slice = idl1;
+
+    Info<< "sliced: " << flatOutput(slice) << nl;
+    Info<< "scratch: " << flatOutput(scratch) << nl;
+
+    // Again, but offset and using intermediate only
+    scratch = -1;
+    labelList::subList(scratch, idl1.size(), 5) = idl1;
+    Info<< "offset: " << flatOutput(scratch) << nl;
+
+
     for (const label val : { 10, 30, 40, 50, 90, 80, 120 } )
     {
         testFind(val, idl1);
diff --git a/src/OpenFOAM/containers/Lists/List/List.H b/src/OpenFOAM/containers/Lists/List/List.H
index 17f33459d4..ebded60c26 100644
--- a/src/OpenFOAM/containers/Lists/List/List.H
+++ b/src/OpenFOAM/containers/Lists/List/List.H
@@ -53,16 +53,12 @@ namespace Foam
 {
 
 // Forward Declarations
-class Istream;
-class Ostream;
-
 template<class T> class List;
 template<class T, unsigned N> class FixedList;
 template<class T, int SizeMin> class DynamicList;
 
 template<class T> class PtrList;
 template<class T> class SortableList;
-template<class T, class Addr> class IndirectListBase;
 
 template<class T> Istream& operator>>(Istream& is, List<T>& list);
 
diff --git a/src/OpenFOAM/containers/Lists/SubList/SubList.H b/src/OpenFOAM/containers/Lists/SubList/SubList.H
index 061028554c..4eddc1abb3 100644
--- a/src/OpenFOAM/containers/Lists/SubList/SubList.H
+++ b/src/OpenFOAM/containers/Lists/SubList/SubList.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -125,12 +125,16 @@ public:
         //- Allow cast to a const List\<T\>&
         inline operator const Foam::List<T>&() const;
 
-        //- Copy assign entries from given sub-list
+        //- Copy assign entries from given sub-list. Sizes must match!
         inline void operator=(const SubList<T>& list);
 
-        //- Copy assign entries from given list
+        //- Copy assign entries from given list. Sizes must match!
         inline void operator=(const UList<T>& list);
 
+        //- Copy assign entries from given indirect list. Sizes must match!
+        template<class Addr>
+        inline void operator=(const IndirectListBase<T, Addr>& list);
+
         //- Assign all entries to the given value
         inline void operator=(const T& val);
 
diff --git a/src/OpenFOAM/containers/Lists/SubList/SubListI.H b/src/OpenFOAM/containers/Lists/SubList/SubListI.H
index 3ec6aa5fa3..53408e3a76 100644
--- a/src/OpenFOAM/containers/Lists/SubList/SubListI.H
+++ b/src/OpenFOAM/containers/Lists/SubList/SubListI.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2017-2020 OpenCFD Ltd.
+    Copyright (C) 2017-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -135,6 +135,14 @@ inline void Foam::SubList<T>::operator=(const UList<T>& list)
 }
 
 
+template<class T>
+template<class Addr>
+inline void Foam::SubList<T>::operator=(const IndirectListBase<T, Addr>& list)
+{
+    UList<T>::deepCopy(list);
+}
+
+
 template<class T>
 inline void Foam::SubList<T>::operator=(const T& val)
 {
diff --git a/src/OpenFOAM/containers/Lists/UList/UList.C b/src/OpenFOAM/containers/Lists/UList/UList.C
index 41dbb8f036..3263d6f0c8 100644
--- a/src/OpenFOAM/containers/Lists/UList/UList.C
+++ b/src/OpenFOAM/containers/Lists/UList/UList.C
@@ -110,8 +110,8 @@ void Foam::UList<T>::deepCopy(const UList<T>& list)
     if (len != list.size_)
     {
         FatalErrorInFunction
-            << "ULists have different sizes: "
-            << len << " " << list.size_
+            << "Lists have different sizes: "
+            << len << " != " << list.size() << nl
             << abort(FatalError);
     }
     else if (len)
@@ -138,6 +138,30 @@ void Foam::UList<T>::deepCopy(const UList<T>& list)
 }
 
 
+template<class T>
+template<class Addr>
+void Foam::UList<T>::deepCopy(const IndirectListBase<T, Addr>& list)
+{
+    const label len = this->size_;
+
+    if (len != list.size())
+    {
+        FatalErrorInFunction
+            << "Lists have different sizes: "
+            << len << " != " << list.size() << nl
+            << abort(FatalError);
+    }
+    else if (len)
+    {
+        List_ACCESS(T, (*this), lhs);
+        for (label i = 0; i < len; ++i)
+        {
+            lhs[i] = list[i];
+        }
+    }
+}
+
+
 // * * * * * * * * * * * * * * * Member Operators  * * * * * * * * * * * * * //
 
 template<class T>
diff --git a/src/OpenFOAM/containers/Lists/UList/UList.H b/src/OpenFOAM/containers/Lists/UList/UList.H
index 1493a88637..1fd97cb99e 100644
--- a/src/OpenFOAM/containers/Lists/UList/UList.H
+++ b/src/OpenFOAM/containers/Lists/UList/UList.H
@@ -68,10 +68,15 @@ namespace Foam
 {
 
 // Forward Declarations
+class Istream;
+class Ostream;
 class labelRange;
+
 template<class T> class List;
 template<class T> class SubList;
 template<class T> class UList;
+template<class T, class Addr> class IndirectListBase;
+
 template<class T> Istream& operator>>(Istream&, UList<T>&);
 template<class T> Ostream& operator<<(Ostream&, const UList<T>&);
 
@@ -342,6 +347,10 @@ public:
         //- Copy elements of the given UList
         void deepCopy(const UList<T>& list);
 
+        //- Copy elements of the given indirect list
+        template<class Addr>
+        void deepCopy(const IndirectListBase<T, Addr>& list);
+
 
     // Member Operators
 
@@ -493,7 +502,7 @@ public:
         typename std::enable_if<std::is_same<bool, TypeT>::value, bool>::type
         inline test(const label i) const
         {
-            return (i >= 0 && i < size() && v_[i]);
+            return (i >= 0 && i < size_ && v_[i]);
         }
 
         //- A bitSet::get() method for a list of bool
diff --git a/src/OpenFOAM/fields/Fields/Field/Field.H b/src/OpenFOAM/fields/Fields/Field/Field.H
index 916c0944a1..056265f3b4 100644
--- a/src/OpenFOAM/fields/Fields/Field/Field.H
+++ b/src/OpenFOAM/fields/Fields/Field/Field.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2011-2016 OpenFOAM Foundation
-    Copyright (C) 2015-2020 OpenCFD Ltd.
+    Copyright (C) 2015-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -101,7 +101,7 @@ public:
 
     // Constructors
 
-        //- Construct null
+        //- Default construct
         //  For temporary fields that are initialised after construction
         inline constexpr Field() noexcept;
 
@@ -374,8 +374,13 @@ public:
         //- Copy assignment
         void operator=(const Field<Type>&);
         void operator=(const tmp<Field<Type>>&);
-        inline void operator=(const UList<Type>&);
-        inline void operator=(const SubField<Type>&);
+
+        inline void operator=(const UList<Type>& rhs);
+        inline void operator=(const SubField<Type>& rhs);
+
+        //- Copy assign from IndirectList
+        template<class Addr>
+        inline void operator=(const IndirectListBase<Type, Addr>& rhs);
 
         //- Move assignment
         inline void operator=(Field<Type>&& rhs);
diff --git a/src/OpenFOAM/fields/Fields/Field/FieldI.H b/src/OpenFOAM/fields/Fields/Field/FieldI.H
index 111c87115e..7cfd44d6f9 100644
--- a/src/OpenFOAM/fields/Fields/Field/FieldI.H
+++ b/src/OpenFOAM/fields/Fields/Field/FieldI.H
@@ -5,7 +5,7 @@
     \\  /    A nd           | www.openfoam.com
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
-    Copyright (C) 2018-2020 OpenCFD Ltd.
+    Copyright (C) 2018-2021 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -172,6 +172,17 @@ inline void Foam::Field<Type>::operator=(const SubField<Type>& rhs)
 }
 
 
+template<class Type>
+template<class Addr>
+inline void Foam::Field<Type>::operator=
+(
+    const IndirectListBase<Type, Addr>& rhs
+)
+{
+    List<Type>::operator=(rhs);
+}
+
+
 template<class Type>
 inline void Foam::Field<Type>::operator=(Field<Type>&& rhs)
 {