 One tactic introduced by Captain John Walker was the "hold-down", where a group of ships would patrol over a submerged U-boat until its air ran out and it was forced to the surface; this might take two or three days.In response to the ineffectiveness of depth charges, the British developed ahead-throwing anti-submarine weapons, starting with Hedgehog.By late 1942, warships started being fitted with the Hedgehog anti-submarine spigot mortar, which fired contact-fuzed bombs ahead of the firing ship while the target was still within the ASDIC beam.