Bittern carried six four-inch guns in three twin mountings, a battery usually listed as anti-aircraft armament. The mounts could depress as well as elevate, so they could engage targets on the surface. The same feature appeared on the four-inch mount installed in the X position of Tribal-class destroyers during anti-aircraft refits. Their performance against small ships gave a treaty-compliant escort useful flexibility against aircraft and surface craft.
Notable Point · 22:51-23:59
The four-inch battery could serve above and on the water
Bittern's six four-inch guns were usually counted as anti-aircraft armament, but their mountings could depress enough to make them useful against small surface targets as well.