At the end of the Second World War, Lend-Lease aircraft such as B-24's and Catalina's, were returned to the USA. As a result, the RAF lacked a long range ASR (air-sea rescue) aircraft. To fill this gap,about fifty Avro Lancaster B.III bombers were modified for this role by Cunliffe-Owen, with three dipole ventral antennas fitted aft of the radome and carrying an airborne lifeboat in an adapted bomb bay. The armament was often removed and the mid-upper turret faired-over, especially in post-war use. Observation windows were added to both sides of the rear fuselage, a port window just forward of the tailplane and a starboard window into the rear access door. A number of ASR 3 conversions were fitted with Lincoln-style rudders.All the conversions featured the H2S ground mapping radar.In 1950 the aircraft were re-roled as the General Reconnaissance (GR), and soon Maritime Reconnaissance (MR) Mk3.
The final operational RAF Lancaster an MR Mk3,was retired on 15th October 1956.