20-MM ANTIAIRCRAFT GUNS
MARK 4 AND MARK 2
Part numbers of the Mark 4 parts are shown in the Mark 4 (OE. or part number) column. Part numbers of the Mark 2 parts are shown in the Mark 2 (item) column.
Parts that are interchangeable between Mark 4 and Mark 2 have their Mark 4 (OE. or part number) and Mark 2 (item) number on the same line.
Parts of an assembly have their names indented under the assembly name.
Where parts have been redesigned and are interchangeable, only the new parts are listed.