sentences:  Among other lessons applied to the design was an armament package better designed to combat U-boats including a twin 4-inch mount forward and 12-pounder aft.15 Canadian frigates were initially fitted with a single 4-inch gun forward but with the exception of , they were all eventually upgraded to the double mount.For underwater targets, the River-class frigate was equipped with a Hedgehog anti-submarine mortar and depth charge rails aft and four side-mounted throwers.