Twin 4” Mounting HA/LA

The gun’s name derives from its four-inch bore and ability to shoot at a high angle (HA) or low angle (LA). At high angle, with the relatively large projectile, it was an excellent anti-aircraft weapon which gained a reputation as the most effective weapon placed on large and small ships. These guns were dual purpose, functioning as both anti-aircraft and anti-surface warfare weapons. It was also reputedly very dependable, with few breakdowns or jamming incidents. 

Tribal-class destroyers initially had one of these mounted second from the rear in the  "Y" position with their other three mountings used with the 4.7" low angle gun. In postwar years Tribal-class ships were refitted, and all four mountings used this gun. They proved highly effective during the Korean war.

The last of the Tribals, HMCS Haida, is a floating memorial ship at Harbourfront in Hamilton, Ontario and still has some guns in working order.

Reference Links:
Haze Gray - Canadian Navy Guns