The Royal Navy used 4-inch, 4.5-inch and 5.25-inch guns in secondary or anti-aircraft roles, while the 4.7-inch was usually associated with destroyers. Nelson and Rodney retained an earlier 4.7-inch anti-aircraft battery, an important exception raised later in the stream. Aircraft carriers complicate the language because their defensive battery was also their largest gun armament. The broader aim was to make the 4.5-inch weapon serve carriers, battleships and destroyers. One dual-purpose calibre would simplify mount choices, training and ammunition supply across several ship types.
Notable Point · 37:21-38:29
The Royal Navy's attempt to standardize secondary guns
The 4.5-inch gun promised to replace several overlapping secondary and destroyer calibres with one dual-purpose ammunition system.