F-4D LORAN Mod - the following information from the excellent site www.f-4nl : AN/ARN-92 LORAN-D equipment was fitted to Pave Phantom F-4Ds. They could be identified by a rather prominent "towel-rail" antenna on the upper rear fuselage behind the rear cockpit. A total of 72 aircraft from blocks 32 and 33 were so equipped. In Vietnam, the primary mission of these Pave Phantom F-4Ds was the seeding of the Ho Chi Minh trail with sensors, which required the precise nighttime navigational capability provided by LORAN.