The Loch class was a class of anti-submarine (A/S) frigate built for the Royal Navy and her Allies during World War II. They were an innovative design based on the experience of three years of fighting in the Battle of the Atlantic and attendant technological advances. Some shipyards had trouble building these larger ships, which led to widespread use of the Castle-class corvette, introduced around the same time. Design The Lochs were based upon the hull of the preceding with increased sheer and flare to improve seakeeping and modified to suit it to mass pre-fabrication, with sections riveted or welded together at the shipyard. Accordingly, as many curves as possible were eliminated, producing a noticeable kink in the main deck where the increased sheer forwards met the level abreast the bridge. The fighting capability of the Loch class was a great jump forward, being based around the new Squid ahead-throwing A/S mortar. Previously, escorts had attacked with depth charges, requiring the attacking vessel to pass over the submerged submarine and drop warheads over the stern. Consequently, the ahead-looking ASDIC (sonar) set lost contact at the vital moment before the weapons were launched, allowing a skilled submarine commander to take successful evasive action. Squid, however, lobbed three , 390 pound warheads up to ahead of the launching vessel falling in a triangular pattern with sides of . As the clockwork fuses detonated the warheads at a depth determined by the ships' ASDIC set, the Squid therefore attacked in full ASDIC contact for greater accuracy and lethality. Two mortars were carried, with the bombs set to explode at different depths in order to create a convergent pressure wave to crush the hull of a submarine. The first successful "kill" was by on 31 July 1944, sinking the . Such was the utility of Squid that depth charge carriage was reduced to only 15, with a single rack and a pair of throwers being carried at the stern, resulting in a clear quarterdeck compared to the eight throwers, two racks and stowage for 100 plus charges in the Rivers. The weapons outfit was completed with a single QF Mark V gun forwards. An oversight in the River design had been to place the gun in the favourable position forward on the shelter deck, with the ahead throwing Hedgehog on the main deck, exposed to the worst of the seas breaking over the fo'c'sle,