Editing Loran-C (section)

===Loran-D and -F===
When Loran-C became widespread, the United States Air Force once again became interested in using it as a guidance system. They proposed a new system layered on top of Loran-C to provide even higher accuracy, using the Loran-C fix as the coarse guidance signal in much the same way that Loran-C extracted coarse location from pulse timing to remove the ambiguity in the fine measurement. To provide an extra-fine guidance signal, '''Loran-D''' interleaved another train of eight pulses immediately after the signals from one of the existing Loran-C stations, folding the two signals together. This technique became known as "Supernumary Interpulse Modulation" (SIM). These were broadcast from low-power portable transmitters, offering relatively short-range service of high accuracy.<ref name=leave>George Galdorisi and Thomas Phillips, [https://books.google.com/books?id=BNSQm05eFy4C&pg=PA391 "Leave No Man Behind"], MBI Publishing, 2009, pg. 391.</ref>

Loran-D was used only experimentally during war-games in the 1960s from a transmitter set in the UK. The system was also used in a limited fashion during the [[Vietnam War]], combined with the Pave Spot [[laser designator]] system, a combination known as Pave Nail. Using mobile transmitters, the AN/ARN-92 LORAN navigation receiver could achieve accuracy on the order of {{convert|60|feet|m}}, which the Spot laser improved to about {{convert|20|feet|m}}.<ref name=leave /> The SIM concept later became a system for sending additional data.<ref>James Caffery, [https://books.google.com/books?id=vbAf4OPAnGoC&lpg=PA5&dq=%22Loran-D%22&pg=PA6 "Wireless Location in CDMA Cellular Radio Systems"], Springer, 2000, pg. 5.</ref><ref>Darrel Whitcomb, [http://www.loran-history.info/Operation_Tight_Reign/PAVE%20NAIL.pdf "PAVE NAIL: there at the beginning of the precision weapons revolutions"] {{webarchive|url=https://web.archive.org/web/20140530065238/http://www.loran-history.info/Operation_Tight_Reign/PAVE%20NAIL.pdf |date=30 May 2014}}</ref>

At about the same time, [[Motorola]] proposed a new system using pseudo-random pulse-chains. This mechanism ensures that no two chains within a given period (on the order of many seconds) will have the same pattern, making it easy to determine if the signal is a groundwave from a recent transmission or a multi-hop signal from a previous one. The system, '''Multi-User Tactical Navigation Systems''' (MUTNS) was used briefly but it was found that Loran-D met the same requirements but had the added advantage of being a standard Loran-C signal as well. Although MUTNS was unrelated to the Loran systems, it was sometimes referred to as '''Loran-F'''.<ref>[https://books.google.com/books?id=ko5KAAAAYAAJ "Proceedings of the Eleventh Annual Technical Symposium"], pg. 7.</ref>