At the outbreak of war, ASW weapons were limited to the depth charge and ASDIC (sonar). The weaknesses of this combination had been known before the start of the war, but the development of a replacement - the ahead-throwing weapon - had not been advanced with much urgency. The Hedgehog spigot mortar arrived in early 1943 and was fitted in older destroyers converted for convoy escort work. Hedgehog was followed by the Squid mortar later in the same year. Although it was trialled on , it was rushed into service in Castle-class corvettes and Loch-class frigates and few destroyers received this weapon before the cessation of hostilities.