The Avro Lancaster Bomber had its origins in an aircraft designed to specification E.13/36 of 1936 which was for a new generation of heavy twin engine medium bombers. This specification resulted in the Handley Page Halifax and the Avro Manchester. The Manchester was designed by Avro’s chief designer Roy Chadwick and was a relatively conventional, but large for its day, mid wing monoplane with low set tail plane and twin fins powered by a pair of Rolls Royce Vulture “X” configuration 24 cylinder engine. The aircraft was protected by a power operated Frazer Nash nose turret armed with a pair of .303 browning machine guns, a similar turret in the tail with four machine guns. Possibly the most unusual feature of the aircraft was its extremely large bomb bay extending along almost half of its underside. The Manchester first flew at Ringway on July 24th 1939 but despite substantial efforts which were put into the development of the design it was consistently let down by the underdeveloped Rolls Royce Vulture engines which had a habit of either breaking con rods, bursting into flames, or both.
The aircraft was placed in production regardless as the RAF was in no position to turn down any aircraft by this time due to the start of the war. Despite this Roy Chadwick remembered conversations he had with Rolls Royce engineers about a new mark of Rolls Royce Merlin engine of the type that was fitted to Spitfire fighters. The power output of this remarkable engine had just been increased dramatically by fitting two stage, two speed supercharges and the comment was made that it would improve the performance of the Manchester dramatically. Chadwick decided there was little point in half measures and decided that the solution was to take off the Manchester’s wings, replace the engines with Merlin’s and so he designed a new centre section wing which mounted a further two Merlin engines before re attaching the original outer wings to the larger centre section. This centre section was really the secret of the Lancaster’s success in that it was built extremely strongly, but remained light. When coupled to the very strong bomb bay structure it made for a very strong aircraft. The Merlin engines were proven and reliable and the addition of two extra engines gave the new aircraft remarkable lifting power.
On the 31st January 1941 the prototype Lancaster BT308 made her maiden flight. Other fairly major changes had been from the Manchester design, notably the installation of a dorsal turret armed with two .303 machine guns and a ventral turret with the same armament. The tail plane configuration was experimented with, the aircraft at one stage having triple tail fins, but this was finally settled with the same configuration as the production Manchester but with much enlarged twin fins. This gave the mid upper gunner a much better field of fire. The initially production model of Lancaster was the B1.
Lancaster Main Facts
The Lancaster benefited from a very clean and economical layout and the compatibility of its engines with other RAF aircraft made it simple and straightforward to service. It was adaptable and perhaps most importantly it was capable of considerable development. With more powerful engines it would haul a heaver load or the same load farther. The main components of the Lancaster went on to form the basis of the Avro Lincoln and the Shackleton which served the RAF into the 1980’s. This adaptability was key to the Dams raid. The aircraft was capable of carrying the Upkeep weapon, its bomb bay was long enough to allow the weapon to be placed on the centre of gravity and the power plants were capable of producing the energy required to spin the mine. Additionally the construction was straightforward and contemporary which allowed the unusual weapon mounted to be fitted.
When converted to carry the Upkeep weapon the aircraft was modified to a new makers type number and was known as the Lancaster type 464 provisioning. Needless to say it was a closely guarded secret and the aircraft produced were given (G) suffix codes meaning that when on the ground they were to be guarded by an armed guard at all times.
The Modifications to the 464 Provisioning aircraft were extensive and covered major items such as the fitting of more powerful engines, removal of the dorsal turret, removal of bomb bay doors, fitting of a wind deflector for the mine, support arms, release mechanism and an ex submarine hydraulic motor and belt drives to spin the mine. Much smaller changes included the fitting of front gunner stirrups to keep his feet out of the bomb aimers face, spent case collecting bags (to stop them falling on the bomb aimers head) and strengthened oleo legs and bomb beams. The design, proving and installation works for all these modifications was carried out in the strictest of secrecy and covered many hundreds of people at tens of companies across the county.
The end result of all this work was an aircraft capable of carrying a very heavy and highly specialised weapon at low level and to be able to position itself at a very precise sped and height over the lakes of Germanys inland lakes. Then to drop it with an accuracy seldom demanded or seen before. It was a great achievement in itself.