The QF 4-inch gun Mk IV was the main gun on most Royal Navy and British Empire destroyers in World War I. It was introduced in 1911 as a faster-loading light gun successor to the BL 4 inch Mk VIII gun. Of the 1,141 produced, 939 were still available in 1939. Mk XII and Mk XXII variants armed many British interwar and World War II submarines.

Mk IV gun

Mk IV armed many British destroyers and some cruisers in World War I. It was used to arm merchant ships in World War II. The guns armed the following warships :

Mk XII and XXII submarine gun

The Mk XII variant was developed for arming submarines from 1918, Mk XXII was developed to arm submarines during World War II. These submarine guns fired a heavier 35 lb projectile from late 1944. Shortly after the end of hostilities, the Mk XXII was superseded in new British submarines by the lighter QF 4 inch Mk XXIII.

Mk XII and XXII equipped submarines

Surviving guns

Weapons of comparable role, performance and era

Sources