Oboe was used extensively by Pathfinder marker aircraft during the Battle of the Ruhr in 1943. In December 1943 Bomber Command began the Battle of Berlin, which was beyond the range of Oboe. For this campaign, Bomber Command was forced to rely on H2S instead, which never was able to provide the consistent accuracy of Oboe. A later development was the Gee-H system, in which the transponder remained on the ground but the transmitter was mounted in the aircraft where the readout was made. This system allowed around 80 aircraft to be guided at the same time. Neither H2S nor Gee-H could provide the accuracy of Oboe, which demonstrated the highest average bombing accuracy of any system in the war.