[Aktungbby]

Actually the sonar cone had little to do with it hence the hedgehog-to alleviate the 'blind spot' of a sonar contact. The Hedgehog became much more successful than depth-charge attacks (the best kill rate was about 25% of attacks whereas depth charges never achieved more than 7%). It initially had a very poor record, although many of the factors had nothing to do with the design of the weapon. USS England sank six Japanese submarines in a matter of days with Hedgehog in May 1944. <<....The group discovered U-853 type IX-C/40 bottomed in 18 fathoms (108 ft; 33 m), and dropped depth charges and hedgehogs during a 16 hour attack. At first the U-boat attempted to flee, and then tried to hide by lying still. Both times it was found by sonar.The morning of 6 May 1945 two K-Class blimps from Lakehurst, New Jersey, K-16 and K-58, joined the attack, locating oil slicks and marking suspected locations with smoke and dye markers. K-16 also attacked with 7.2-inch rocket bombs. Numerous depth charge and hedgehog attacks from Atherton and Moberly resulted in planking, life rafts, a chart tabletop, clothing, and an officer's cap floating to the surface. With the loss of all 55 officers and men, U-853 was one of the last U-boats sunk during World War II. and, with U-881, the last to be sunk in US waters. Atherton and Moberly received credit for the kill. <U-853 now at 121 feet thirteen miles off Block Island, Rhode Island [wiki]http://www.aquaexplorers.com/u-853_shipwreck.htm The U-boats' sinking was after Donitz's transmitted order to cease offensive operations on May 1 1945!??