LORAN

thumb|right|The AN/APN-4 was an airborne LORAN receiver used into the 1960s. It was built in two parts to match the UK's Gee system, and could be swapped with Gee in a few minutes. LORAN (Long Range Navigation) was a hyperbolic radio navigation system developed in the United States during World War II. It was similar to the UK's Gee system, but operated at lower frequencies in order to provide an improved range up to 1,500 miles (2,400 km) with an accuracy of tens of miles. It was first used for ship convoys crossing the Atlantic Ocean, and then by long-range patrol aircraft, but found its main use on the ships and aircraft operating in the Pacific theater during World War II.

LORAN, in its original form, was an expensive system to implement, requiring a cathode ray tube (CRT) display and a well-trained operator. This limited use to the military and large commercial users. Automated receivers became available in the 1950s, but the same improved electronics also opened the possibility of new systems with higher accuracy. The United States Navy began development of Loran-B, which offered accuracy on the order of a few tens of feet, but ran into significant technical problems. The United States Air Force worked on a different concept, Cyclan, which offered longer range than LORAN and accuracy of hundreds of feet. When the Air Force turned their attention to inertial navigation systems, the Navy took over Cyclan and renamed it Loran-C. The United States Coast Guard took over operations of both LORAN systems in 1958.