Short answers, pulled from the story.
Squid was a British ship-mounted anti-submarine weapon consisting of a three-barrelled 12-inch mortar that launched depth charges ahead of the attacking vessel. It was designed to sink enemy submarines by creating a pressure wave above and below the target simultaneously. It replaced the earlier Hedgehog system and was itself later replaced by the Limbo system.
Squid achieved one submarine kill for every 2.9 attacks, compared to a ratio of 60.5 to 1 for conventional British depth charges in World War II. Post-war trials confirmed Squid was nine times more effective than conventional depth charges. Over the course of the war it was credited with sinking 17 submarines in 50 attacks.
The first successful use of Squid in combat was by HMS Loch Killin on the 31st of July 1944, when she sank a submarine. Squid had first entered service in May 1943 aboard HMS Ambuscade, with the first production unit installed on HMS Hadleigh Castle.
Royal Canadian Navy Captain Kenneth Adams and some other officers opposed fitting Squid to escorts because installing the mortar required removing guns, leaving the ships unsuitable for fleet actions. The concern was that anti-submarine specialisation would reduce a vessel's general combat capability.
The Royal Navy fired Squid in service for the last time in April 1977, when the Type 61 frigate Salisbury discharged the weapon. The Swedish Navy continued using Squid until 1982, when the Östergötland-class destroyers were decommissioned.
Examples of the Squid mortar are on display at the Explosion! Museum of Naval Firepower in Gosport, Hampshire, and at Devonport Naval Base. A preserved ship fitted with the system is at the Historic Dockyard in Chatham, Kent, and further examples can be seen in Hamilton, Ontario and at the naval museum in Malacca, Malaysia.