When I were a lad there were a number of co-located TACAN and VORs - WAL/WAZ, OTR/OTZ, STN/STZ. The TACANs (which also supplied the DME function) had the 'Z' on the end to show that they were not exactly co-located. To have the same ident they both have to be within ??? metres.
As time went by and military route-flying aircraft were fitted with VOR receivers the TACANs were removed and DMEs were put in with the VORs. In the UK now TACAN is mainly an airfield approach and orientation aid. However there is still a TACAN 'airways' structure (info cribbed from another thread):
Details of the TACAN route structure can be found at:
http://www.ais.org.uk/aes/pubs/aip/pdf/enr/26030502.PDF
you need to register to get to the site but it's free.
TACAN is more accurate because, instead of having a single rotating reflector producing an AM cardioid (or is it a limacon?), TACAN has 9 extra rotating reflectors. Rather than using an omnidirectional FM signal, TACAN uses timing pulses: a 'Master Reference Burst' and others that tie in with the small reflectors. The only problem this can lead to is a 40° bearing error which can be a bit embarrassing.