QF 4 inch Mk XIX naval gun

The QF 4-inch Mk XIX gun was a British low-velocity 4-inch 40-calibre naval gun used to arm small warships such as Bathurst and Castle class corvettes and some River-class frigates in World War II, mainly against submarines.

Description
It succeeded the higher-velocity World War I-era BL 4-inch Mk IX (typically deployed on Flower class corvettes in the escort role), increasing the shell weight from 31 to 35 pounds and its high-angle mounting added some anti-aircraft capability and allowed it to fire starshells to illuminate the battle area at night.

Surviving examples

 * On HMAS Castlemaine at Williamstown, Victoria, Australia.
 * On the parade ground at the Irish Naval Service Base, Haulbowline, Co. Cork, Ireland