Gee-H, sometimes written G-H or GEE-H, was a radio navigation system developed by Britain during World War II to aid RAF Bomber Command. The name refers to the system's use of the earlier Gee equipment, as well as its use of the "H principle" or "twin-range principle" of location determination. Its official name was AMES Type 100. Gee-H was adapted by RCA into the US wartime SHORAN system with improved accuracy. The same basic concept remains in widespread use today as the civilian DME system.