Editing Battle of the Atlantic (section)

===Ahead-throwing weapons===
[[File:The Battle of the Atlantic 1939-1945 A31000.jpg|thumb|[[Hedgehog (weapon)|Hedgehog]] anti-submarine mortar mounted on the forecastle of the destroyer {{HMS|Westcott|D47|6}}]]

At the start of World War II, the depth charge was the only weapon available to a vessel for destroying a submerged submarine. Depth charges were dropped over the stern and thrown to the side of a warship travelling at speed. Early models of ASDIC/Sonar searched only ahead, astern and to the sides of the anti-submarine vessel that was using it: there was no downward-looking capability. So there was a time lag between the last fix obtained on the submarine and the warship reaching a point above that position. Then the depth charges had to sink to the depth at which they were set to explode. During those two delays, a capable submarine commander would manoeuvre rapidly to a different position and avoid the attack. The depth charges then left an area of disturbed water, through which it was difficult to regain ASDIC/Sonar contact. In response to this problem, one of the solutions developed by the Royal Navy was the ahead-throwing anti-submarine weapon—the first of which was Hedgehog.

====Hedgehog====
Hedgehog was a multiple [[spigot mortar]], which fired contact-fused bombs ahead of the firing ship while the target was still within the ASDIC beam. These started to be installed on anti-submarine ships from late 1942. The warship could approach slowly (as it did not have to clear the area of exploding depth charges to avoid damage) and so its position was less obvious to the submarine commander as it was making less noise. Because hedgehog only exploded if it hit the submarine, if the target was missed, there was no disturbed water to make tracking difficult—and contact had not been lost in the first place.{{sfn|Morison|2001|pp=211–212}}

====Squid====
[[Squid (weapon)|Squid]] was an improvement on 'Hedgehog' introduced in late 1943. A three-barrelled mortar, it projected {{convert|100|lb|kg|abbr=on}} charges ahead or abeam; the charges' firing pistols were automatically set just before launch. The more advanced installations linked Squid to the latest ASDIC sets so that the weapon was fired automatically.{{sfn|Costello|Hughes|1977|p=308}}