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Rare document document relating to Lancaster III ED.765, one of the bombers used in Barnes Wallis’ practice runs for the Dambusters raid, is estimated at £2000-3000 in Tennants' auction.

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In the June 13 Militaria & Ethnographica sale in Leyburn a document relating to Lancaster III ED.765, one of the bombers used in Barnes Wallis’ practice runs, is estimated at £2000-3000.

The rare Air Ministry Design Certificate for Flight Trials (Form 1187) details specification, contractor, and flight tests by Captain HA Brown from Woodford Aerodrome. The four-propeller Lancaster bomber was made by Avro, the British aircraft manufacturer which had been established in 1915 in Manchester.

The certificate is signed by Avro’s chief designer and engineer, Roy Chadwick – a rare example of his signature.

This particular Lancaster bomber was assigned to 617 Squadron, who so famously carried out Operation Chastise in May 1943 aka the Dambusters as they became later known. While not actually taking part in the mission, ED. 765 was used by the squadron in practice runs under the eye of Wallis, designer of the ‘bouncing bomb’. The aircraft crashed during a training flight in August 1943 but all members of the crew survived.

The document is to be sold alongside three further Air Ministry Design Certificates for Flight Trials for Lancaster bombers, and accompanying letters and photographs. These rare documents were saved by an engineer at the Avro factory – the majority of the company documents were destroyed.

Bomb release button

Last year Northamptonshire auction house JP Humbert (now Humbert & Ellis) sold several significant Dambusters lots including the Bakelite bomb release button pressed by bomb aimer John Fort on board Lancaster bomber ED 906 AJ-J, the fifth aircraft to attack the Möhne Dam, which was piloted by Squadron Leader David Maltby.

On July 1 it took a hammer price of £39,500 against an estimate of £25,000-40,000.

Manchester to Lancaster

Avro had been developing the Manchester bomber but even before it flew on operations, Chadwick realised that it would have serious problems and made plans for its modification. He added 12ft to the wingspan and replaced the two Vulture engines with four of the proven Rolls Royce Merlins V-12s and the Lancaster was born.

This design made its maiden flight in January, 1941. The Lancasters were built at Woodford Aerodrome by Avro. Recently, Gloucestershire saleroom Dominic Winter sold at auction an original Avro hangar which had stood at Woodford.