There was a period of just two months between approval being given in March 1943 and the actual Dambusters raid on May 16/17, 1943.
So, there was an enormous amount of work for the mechanics to do in order to adapt a whole squadron of standard Lancaster bombers to fit a weapon that had never been delivered before.
The inventor of the bouncing bomb, Barnes Wallis, called on the expertise of Roy Chadwick, the inventor of the Lancaster Bomber, to help him make the necessary modifications to the planes.
Probably the single most important modification that needed to be made was the support brackets, or calipers, that were needed to hold the Upkeep mine in place, and a hydraulic motor to impart spin on the weapon before it was dropped.
However, there were a series of other adjustments too, including a deeper bomb aimer's blister, no mid-upper gun turret and the replacement of bomb doors by front and rear fairings.
These Lancasters were called Type 464 (provisioning) and the plans were drawn up by Chadwick himself. A team of fitters worked day and night to make sure that all the aircraft were ready in time. One of the fitters said that, "We worked 12 hour shifts, seven days a week to get them ready. The atmosphere was exciting, electric."
The source of the engine to spin Upkeep came from an unusual source, as revealed by air frame mechanic Sandy Bonser: ‘For the arms to work they had to be fitted with hydraulic rams, then another modification was needed to get the bomb spinning. This was a headache.
They wanted a motor strong enough and small enough to fit just rear of the centre section, where the old bomb doors finished. They managed to get a motor from a submarine – this worked perfectly.’
However, things didn't always go to plan and last minute modifications were common, for instance when Vickers draughtsman Norman Boorer had to take a sledgehammer to one of the bomb bays.
Wallis was cross: "What are you going to do about it?" he said. "We've got to get this bomb in the Lancaster today."
"I'll go and get a sledgehammer," replied Boorer.
This blog is dedicated to the memory of Sergeant Thomas Jaye, a navigator with 617 Squadron on the Dambuster raid, who was killed in action on May 17, 1943.