H2S was the first airborne, ground scanning radar system. It was developed in Britain during World War II for the Royal Air Force and was used in various RAF bomber aircraft from 1943. It was designed to identify targets on the ground for night and all-weather bombing, allowing attack outside the range of the various radio navigation aids like Gee or Oboe which were limited to about 500 km. The early variants of the transmitter/receiver equipment were officially known as TR3159 (H2S Mk I/ASV VIB) or TR3191 (H2S Mk II).