On March 15th 1943 Sir Arthur Harris ordered Air-Vice Marshall Cochrane, the AOC of 5 Group to organise the operation against the dams. Harris clearly specified that an entirely new squadron must be formed for the job and that it was meant to be led by Wing Commander Guy Gibson, currently the commander officer of 106 squadron flying Lancasters at Syreston who had reached the end of his operational tour and was posted to 5 Group headquarters expressly with the task of writing a book on the air crew in bomber commander. However he was summoned before the AOC and asked he would be willing to lead a very important operation. Gibson agreed. Gibson was told that he would need to form a new squadron for a special operation and that it would be extremely dangerous. He was given 5 Group’s main airfield at Scampton and was given a free hand to choose whichever crew he required. The urgency of the situation was also stressed to Gibson. Gibson could not however be told what the target was.
On March 17th a new squadron was formed, known initially as X Squadron. It was not until some days later that the Air Ministry allocated it the number 617. The squadron was officially formed on the 21st March and on that date the first of Gibson’s hand picked crews began assembling at their new base. Please note that many sources record Gibson as hand picking the crews but this is not the case they arrived as a result of his picking some crews known to him and who had served before with him on 106 Sqn but the bulk of the crews were volunteers responding to a written invitation from No 5 Group Headquarters to all Squadrons in the Group calling for volunteers to form a Squadron for a special operation. Some were simply posted in. It was a result of this circular that Les Munro and possibly McCarthy and Maltby, volunteered to become members of what was to be 617 Sqdn. Gibson would not have personally known the bulk of the pilots and their crews that initially formed the Sqdn. The crews came from several Commonwealth countries, Great Britain, Australia, New Zealand, Canada and also the USA. By the 27th over 700 personnel including ground staff had arrived at the station and work had begun on the aircraft. Gibson gave a welcome talk to the aircrew and stressed the fact that they were a very unusual squadron and that security was paramount.
There were still a number of important factors in the operation which had not been resolved. It was not known how easy it would be to fly at the required 150ft about the still waters of a lake at night and it was not known how accurate the radio altimeters would be. Navigation was going to be difficult as the whole operation was to be carried out at night at low level and lastly no firm plan had been made for gauging the distance from the dam that would allow the aircraft to drop the bomb at the correct distance of between 400-450 yards from the dam face. Training would give the answers to these problems. The operational staff at 5 Group set too, to bring together the various strands of the operations. Production of the bombs was put in hand and all resources were given to Vickers to convert the Lancasters to the new specification required for carrying the weapon.
Photo recognisance of the dam took place and produced several shocks, not least by variations in the positions of flak guns at or near the dams and at the last minute a series of strange vertical objects were spotted arriving alongside the roadway which ran across the Möhne dam. Photographic interpretation officers could not ascertain exactly how tall these objects were or what shape they were. It later transpired that they were false trees that the Germans had bought in, in an attempt to soften and camouflage the distinctive outline of the dam.
Gibson and his flying commanders were asked in the light of their experience to finalise the tactics to be used for the raid. This information was pored over at length, and several drafts were prepared but these resulted in the draft operational order (B976) and with the operation to take place at “the first suitable opportunity”. Three last resort targets were added to the plan, Target D- the Lister dam, Target E the Ennepe with Diemel having replaced the Henne as Target F.
The die was now cast and the operation would take place.