A
tactical air navigation system, commonly referred to by the
acronym TACAN, is a
navigation system used by military aircraft. It provides the user with bearing and distance (slant-range) to a ground or ship-borne station. It is a more accurate version of the
VOR/
DME system that provides
bearing and
range information for
civil aviation. The DME portion of the TACAN system is available for civil use; at
VORTAC facilities where a VOR is d with a TACAN, civil aircraft can receive VOR/DME readings. Aircraft equipped with TACAN
avionics can use this system for en route navigation as well as non-precision approaches to landing fields. The
space shuttle is one such vehicle that was designed to use TACAN navigation but later upgraded with
GPS as a replacement.