HE Avro Lancaster was the most famous and widely used four-engine British bomber of WW II. Oddly, however, it didn't originate as a four-engine design. In 1937, the British Air Ministry issued a requirement for a heavy bomber to be powered with two new and still experimental 1,760hp Rolls-Royce Vulture engines.
A.V. Roe and Co., Ltd., of Newton Heath, Manchester, won the order with its Model 679—named "Manchester" by the Royal Air Force. The prototype was first flown in July 1939. The program was seriously delayed by a German air raid, and it was then ended by the shortcomings of the still-troublesome Vulture engine (priorities for the Merlin engine prevented Rolls-Royce from perfecting the Vulture). Only 200 Manchesters were built, some of which saw action over Germany (February 1941 to June 1942).
To save the Manchester program, Avro developed a four-engine modification of the basic airframe. It had a wider center section and longer wing panels for use with the 1,145hp Rolls-Royce Merlin engine (as used in the Hawker Hurricane and Supermarine Spitfire fighter). These changes increased the wingspan from 90 feet, 1 inch to 102 feet for the same 50,000-pound gross weight. The converted airframe, originally named "Manchester III," first flew on January 9,1941. The Air Ministry was pleased with its performance and immediately ordered the revised design into production designated as the "Avro Model 683 Lancaster."
Demand was more than Avro could handle, so production of an eventual 7,374 Lancasters was distributed among two Avro plants and one Canadian and four other British manufacturers. The first production Lancaster I, powered by 1,260hp Merlin XX engines, flew on October 31,1941. The short time it took to move the Lancaster from prototype to production can be attributed to its being essentially a modified Manchester, not a completely new design.
Both offensively and defensively, the Lancaster I was a formidable machine, with a gross weight of 65,000 pounds—greater than that of the American Boeing B-17. It could usually carry 7,000 pounds of bombs and was defended by four powered machine-gun turrets with 10 to 12,303-caliber guns. Lancasters first went into action in March 1942 and were the backbone of the British heavy bomber fleet for the rest of the war.
As a precaution against a shortage of Merlin engines, a Lancaster II using the 1,650hp Bristol Hercules VI air-cooled radial engine was developed. A large production order was placed with one of the subcontractors, but the anticipated Merlin shortage didn't materialize, so the Lancaster II order was progressively reduced until only 300 were delivered. Lancasters that had Merlin engines built in the U.S. by Packard were designated "Lancaster III" (2,990 produced). The 430 built in Canada with Packard Merlins were identified as "Lancaster X."
Intermediate marks identified various improved ver sions: Marks IV and V were special long-range versions; Mark VI had improved 1,750hp Merlins; and Mark VII had 1,620hp Merlins but a gross weight of 68,000 pounds. Marks VIII and IX
The Lancasters were used primarily as night bombers in the Allied program that bombed Germany "around the clock"—the Americans attacking by day, the British by night. Specially modified Lancasters were used on some spectacular missions, such as the breaching of the Mohne and Eder dams in May 1943 and the sinking of the battleship Tirpitz, hidden in a Norwegian fjord, with a single 12,000-pound bomb in November 1944. Special Lancasters modified to carry 22,000-pound Grand Slam bombs had gross weights of 72,000 pounds.
Lancasters remained in service with the Royal Air Force until February 1954 and with the Royal Canadian Air Force until April 1964. Only two fly-able Lancasters remain today.
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