From failure to success. The four engines Avro type 683 Lancaster was developed from the disappointing twin-engine Manchester, which suffered from engine fires caused by its unreliable Rolls Royce Vulture engine-installation.
However, the basic Manchester airframe was of sound design. A logical solution was to increase the wingspan and replace the two Vultures with four Merlin engines. The engine-installation originally developed by Rolls-Royce for the Beaufighter II, was quickly adapted and fitted in graceful underslung nacelles. The prototype BT308 made its first flight on January 9th, 1941 and it soon proved to be an excellent aircraft with good handling and high load capability. Initially designated Manchester III, it was soon renamed Lancaster. The general outline of the Lancaster remained the same throughout production, apart from the MK II which was used Bristol Hercules radial engines, in case a shortage of the Merlin should arise. The Mk 1 and III were similar, differing only in the type of Merlin engine fitted. In the case of the Mk III, the Packard built Merlin 28 was utilised. The Lancaster began to equip bomber squadrons in early 1942, where it quickly became the backbone of RAF Bomber Command.