 The ship mounted four 45 @-@ calibre quick @-@ firing ( QF ) 4 @.@ 7 @-@ inch Mk IX guns in single mounts , designated ' A ' , ' B ' , ' X ' , and ' Y ' from front to rear . For anti @-@ aircraft ( AA ) defence , Boreas had two 40 @-@ millimetre ( 1 @.@ 6 in ) QF 2 @-@ pounder Mk II AA guns mounted on a platform between her funnels . She was fitted with two above @-@ water quadruple torpedo tube mounts for 21 @-@ inch ( 533 mm ) torpedoes . One depth charge rail and two throwers were fitted ; 20 depth charges were originally carried , but this increased to 35 shortly after the war began . The ship was fitted with a Type 119 <unk> set to detect submarines through sound waves <unk> into the water that would reflect off the submarine . 
