heavy loads to be carried by the airborne troops, and the possibility that they could be widely dispersed if they were dropped by parachute, the airborne troops would still be trained for a possible parachute insertion if the landing zone for the gliders was found to be unsuitable. Because of the complicated and technical nature of the operation, which would see the plant rigged with explosives and then detonated, it was believed that a minimum of twelve to sixteen men was required, and that they would all have to be skilled engineers. The important nature of the operation also led to the force being doubled in order to duplicate it, to ensure that even if half of the force were killed, the survivors would have the necessary skills to complete the operation. The selected troops were volunteer parachutists chosen from the sappers of 9th Field Company (Airborne) Royal Engineers and 261st Field Park Company (Airborne) Royal Engineers attached to 1st Airborne Division, because the only parachute-trained Royal Engineers unit in existence at the time, 1st Parachute Squadron Royal Engineers, was already deployed in North Africa with 1st Parachute Brigade. Both of the duplicated units that were to participate in the operation were to be commanded by officers from the Royal Engineers; the first by Lieutenant A.C. Allen and the second by Second-Lieutenant M.D. Green, who was later replaced by Lieutenant D.A. Methven when he was injured during a training accident three days before the operation was to begin. The Royal Air Force unit selected to transport the sappers was 38 Wing, which was commanded by Group Captain T.B. Cooper; it was provided with a special allotment of three Handley Page Halifax heavy bombers for the operation, which were the only British aircraft in existence at the time which were capable of towing Horsa gliders the distance required and then returning to their base. The SOE agents selected a landing zone for the sappers, which was approximately from the Norsk Hydro plant and could not be observed by German patrols. The plan for the operation called for the sappers to land in the two gliders at the landing zone, guided in by the SOE agents equipped with Eureka radio beacons. Once they had successfully landed, the sappers would be escorted to the plant by the SOE agents, demolish the plant and its stocks of heavy water, and then cross the Norwegian