The standard asdic set fitted to most British frigates and destroyers was the type 144. This had a range of 3000 yards and a narrow beam width which searched in 10 degree steps over an area 80 degrees each side of the bow. The underside of the beam had a cutoff of 1 in 3 slope so that if contact was lost at 300 yards, the depth of the target was 300 feet ! At this stage a second transducer, Q, whjch was set at a steeper angle maintained contact for the last stages of the attack.
With the introduction of ahead throwing mortars a further asdic set was introduced the type 147 which scanned a fan shaped area in a vertical plane in order to determine the accurate depth of the target and set the depth on the bombs at the moment of firing.