Events now began to gather pace, on the morning of May 12th more mines had appeared in the bomb dump at Scampton. On the 13th more, and on the 14th yet more, with each new delivery ‘Doc’ was out marking each mine with his ‘secret’ code. Once again he was concealing something, these new arrivals were ALL live, instead of concrete, each one contained 6,600 lbs of Torpex D High Explosive. However the code had done it’s job, the armaments crews had adopted the attitude that every mine was potentially ‘live’ and treated them accordingly. Also on the 13th, the final Type 464‘P’ Lancaster ED937 arrived, this was given the code AJ – Z and was assigned to Maudsley as a temporary replacement for his damaged aircraft. On the afternoon of the 13th, the one and only ‘live’ drop was carried out with an Upkeep mine, this was performed by ED825 the original Type 464 ‘P’ conversion, stationed at Vickers Armstrong as a test bed aircraft. The mine was dropped 75 miles off the coast of Broadstairs Kent, it performed flawlessly and ‘ran’ for almost 800 yds before sinking below the water, there followed a huge explosion and a great flume of water was blasted 100 feet into the air. On the evening of the 14th , 617 Squadron embarked on what would be the final, near full scale, dress rehearsal, flying to 2 lakes and making a series of dummy attacks. Flt Lt David Maltby had taken ED609 / AJ – J to Avro at Woodford for minor repairs and, returning late, missed the ‘show’. Several other crews flew borrowed or 'standard' aircraft as their own planes were grounded for last minute work. Even as the dress rehearsal was underway, across the Channel a lone Mosquito PR raced across the Ruhr, photographing the target sites. Avoiding flak and evading fighters it flew home with it’s precious photo cargo. When developed these showed that, as suspected, a week of heavy rain in the area had filled the reservoirs to near capacity. Between them, the Mohner and the Eder Dams alone held back almost 336 million gallons of water. At 09:00 hrs on Saturday 15th May a signal arrived at Bomber Command Headquarters. From : Assistant Chief of the Air Staff, AVM Norman Bottomley. To : Bomber Command Headquarters. ‘ Op CHASTISE’ Immediate attack of targets “X” , “Y” , and “Z” approved. Execute at earliest possible opportunity…… end This short, simple message set in motion a frantic 36 hours, both at Scampton and at No5 Group Headquarters at Grantham. AVM Cochrane drove to Scampton to inform Station Commander Whitworth that the operation was to take place the following night. Barnes Wallis began the journey to Scampton to monitor the arming and loading of the mines and also to prepare for the mission briefing. Gibson returned with Cochrane to Grantham and together they discussed final details of the operation. By 18:00 hrs Gibson was back at Scampton, were he and Barnes Wallis met Whitworth at his house and, along with Flight Leaders Young and Maudsley, Squadron Bombing Leader Bob Hay and Flt Lt Hopgood, who would take over as Mission Leader should ‘anything happen’ to Gibson, conducted an initial briefing………..