Avro 684

The Avro 684 was a proposed British high-altitude heavy bomber of the Second World War, based on Avro's Lancaster. Because heavy bombers were increasingly vulnerable, Avro completed a brochure in August 1941 for the Avro 684 Stratosphere Bomber, and Roy Chadwick chose to drop defensive armament and rely on altitude and speed. It was essentially a Lancaster with a pressure cabin in the nose and an unusual master-slave engine layout, in which four wing-mounted Rolls-Royce Merlin XX engines were supercharged by a fuselage-mounted slave Merlin 45 driving a large supercharger. At 60,000 lb all-up weight it was expected to reach a service ceiling of 42,000 ft, but design was suspended because of constant Lancaster development and work on the York transport.