Official testing at Boscombe Down during March found that the elevators and ailerons responded well at either end of an I.A.S. range of 100 to 290 mph, but rudder pressure did increase with speed. The strong tendency to swing to port during takeoff was solved by advancing the port-outer throttle and raising the tail quickly, to allow the pilot to bring the rudders into play. In May the second prototype, DG595, took to the air. In contrast to BT308, she carried both mid-upper and ventral turrets and a newly designed and enlarged twin tail configuration which discarded the center fin. New 1,280 HP Merlin XX engines had been installed in place of the earlier Merlin Xs. The RAF now had a bomber with which it could wage war in Germany. There would be no more talk around the squadrons about reunions in POW camp!
First operational RAF squadron to be equipped with Lancasters was No 44, which used them operationally for the first time on March 3,1942 laying mines in the Heligoland Bight. Defended by ten machine-guns and carrying a maximum bomb load of 6,350 kg (14,000 lb). The Lancaster was, and soon proved itself to be a formidable weapon in the hands of the RAF, which had, by mid 1942, learned a great deal about night bombing operations over Europe. By comparison with contemporary four-engined bombers it was statistically the most effective, dropping 132 tons of bombs for each aircraft lost on operations; the corresponding figure for the Halifax and Stirling were 56 and 41 tons respectively. The Lancaster was so right, from the beginning, that there were very few changes in airframe design during its wartime service. Improved power plants, however, provided steadily improving performance: the Lancaster VII, for example, with 1,207 kW (1,620 hp) Merlin 24 engines, had a maximum takeoff weight of 30,844 kg (68,000 lb) by comparison with the 22,680 kg (50,000 lb) of the early Is. Bomb load changed considerably, the cavernous bomb bay being designed originally to carry bombs of up to 4,000 lb, with a total bomb load of 6,350 kg (14,000 lb); it was modified progressively to carry the 22,000 lb Grand Slam bomb.
The Lancaster will be remembered for its part in two spectacular operations: the breaching of the Mohne and Eder dams on the night of May 16-17,1943 by No 617 Squadron (led by Wing Cdr. Guy Gibson); and the sinking of the German battleship Tirpitz Its contribution to victory in World War II is best measured, however, by the total of 608,612 tons of bombs delivered, which represented Two-thirds of the total bomb load dropped by the RAF from the time of its entry into service. A total of 7,366 Lancasters were built (including Mk Xs in Canada) and the type remained in front-line service with the RAF until 1954. Canada had some photo-reconnaissance Lancasters in service in 1964.