 By October 1940 , the ship 's AA armament was increased when the rear set of torpedo tubes was replaced by a 3 @-@ inch ( 76 @.@ 2 mm ) ( 12 @-@ pounder ) AA gun and ' Y ' gun was removed to compensate for the additional depth charges added . Boreas was converted to an escort destroyer in late 1943 with the replacement of the 12 @-@ pounder high @-@ angle gun with additional depth charge stowage . The 2 @-@ pounder mounts were replaced during the war by 20 @-@ millimetre ( 0 @.@ 8 in ) Oerlikon <unk> . Four additional Oerlikon guns were added in the forward superstructure for a total of six guns . 
