task of fitting H2S to the Stirling, and in early 1943 he managed to obtain a single 3 cm magnetron from Herbert Skinner's AI group working on the Boeing. He had it working in the H2S electronics in a benchtop set on 7 March 1943, and then quickly fit it to Stirling N3724 to make its first flight on 11 March. Testing showed the unit had very short range, and could not be used effectively over altitude. Further work was delayed by the need to fit the existing 10 cm sets to operational aircraft. Bomber Command began a series of large-scale raids on Berlin on the nights of 23/24 August, 31 August/1 September and 3/4 September 1943. H2S was found to be largely useless on these missions; the city was so large that picking out features proved very difficult. On 5 September, Saward visited the H2S team and showed them photographs of the PPI displays from H2S over Berlin. On the range setting, used during the bomb run, returns covered the entire display and there were no clear outlines of large objects on which to navigate. This was a surprise given the excellent results over Hamburg. After much argument among teams within the TRE on how to address this problem, on 14 September the team began working on an official version of H2S working in the X band. By this time the American MIT Radiation Laboratory facility was also entering the fray. They had decided to move directly to the 3 cm wavelength, calling their unit H2X. It was being deployed on American bombers by October 1943. By June there was an ongoing debate in the UK whether to continue the development of their own 3 cm H2S sets or simply use the American units when they became available. The suggestion was made that the existing H2S Mk. II units should be converted to X band, and the Americans should work on 3 cm ASV instead. This was followed by a 7 June meeting in which TRE management decided to press for three squadrons of 3 cm H2S by the end of the year. Lovell's team considered this to be basically impossible. Instead, they hatched a private plan to build and install a total of six sets which would equip Pathfinder Force Lancasters by the end of October. Work continued on what was now known as H2S Mk. III, and