A RARE document detailing the famous Dambuster operation’s practice flight is going under the hammer.

Tennant’s of Leyburn is auctioning off the Air Ministry Design Certificate for Flight Trials relating to Lancaster III ED.765, one of the bombers used in the Operation Chastise practice runs.

The certificate details specification, contractor, and flight tests by Captain H A Brown.

The Lancaster bomber was made by the British manufacturer, Avro, and the certificate is signed by its chief designer and engineer, Roy Chadwick – a rare example of his signature.

This particular Lancaster was assigned to 617 Squadron, who so famously carried out the German ‘Dambusters’ attacks in May 1943.

Whilst not actually taking part in the mission, ED. 765 was used by the squadron in practice runs under the eye of Barnes Wallis, designer of the ‘bouncing bomb’.

It is to be sold with an estimate of £2,000 to £3,000 on June 13.