 The ship mounted four 45 @-@ calibre 4 @.@ 7 @-@ inch Mk IX guns in single mounts designated ' A ' , ' B ' , ' X ' and ' Y ' from front to rear . For anti @-@ aircraft ( AA ) defence , Duncan had a single 12 @-@ pounder AA gun between her funnels and two quadruple Mark I mounts for the QF 0 @.@ 5 @-@ inch Vickers Mark III machine guns mounted on the sides of her bridge . She was fitted with two above @-@ water quadruple torpedo tube mounts for 21 @-@ inch 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 . In 1936 , the 12 @-@ pounder was replaced by two QF 2 @-@ pounder Mk II AA guns . Sometime after the Dunkirk evacuation , the ship 's rear torpedo tube mount was removed and replaced by a 12 @-@ pounder AA gun and the quadruple 0 @.@ 5 @-@ inch machine guns were replaced by 20 @-@ millimetre ( 0 @.@ 79 in ) Oerlikon AA guns . 
