The Avro Lancaster was by far the finest night bomber of World War II and the crowning achievement of British wartime aviation. It began life as the twin-engined Manchester bomber which proved a failure but was then re-designed with four engines and a longer wingspan. It entered service in early 1942 with initial bombing missions being considerably successful and which would prove the Lancaster to be the finest aircraft of its kind: a very low loss ratio and the ability to be adapted to carry a variety of ordinance, including the massive Tallboy and Grand Slam bombs, as well as other innovative weapons like Barnes Wallis' famous bouncing bombs. It was Lancasters of the famed No. 617 Squadron which dropped the bouncing bombs in daring raids against German damns in the Ruhr valley. It was also Lancasters which crippled and sank the battleship Tirpitz in 1944. By war's end, Lancasters were equipped with some of the most advanced bombing aids like Gee and H2S and were in fact more accurate than the USAAF's day bombers as well as having a higher survival rate than any other British heavy bomber. Overall, Lancasters flew 156,000 missions and dropped 608,612 tons of bombs, they were to have formed the main strength of the Commonwealth Tiger Force to be sent against Japan but were replaced shortly after the war by the Lincoln.

First flown on 9 January 1941, the Avro 683 entered service a year later as the Mk. I variant which was the most widely built version of this famous bomber. Subsequent variants like the Mk. II and III featured more powerful engines and became the mainstay of Bomber Command during the last years of the conflict. The Mk. I (Special) was adapted to carry exceptionally heavy bombs like the 12,000-lb Tallboy, 22,000-lb Grand Slam and Barnes Wallis' bouncing bombs. Other variants included the Mk. VI with improved Merlin 87 engines (with 4-bladed propellers), the Mk. VII with a revised dorsal turret, and the modified Mk. I (FE) for service in the Far East. Some Lancasters based on the Mk. III were built in Canada by Victory Aircraft and were designated Mk. X.