Gene Whitt wrote:

The main push for a KNOT measure of aircraft speed came from the use of DME
in military aircraft which was always slant range to a
military VOR known as a TACAN."


Picking at nits: The azimuth portion of a TACAN facility is not a military VOR;
rather it is a somewhat different method of providing bearing and operates at
UHF frequencies.

There was quite a contest between TACAN and VOR/DME for the military. The Air
Force was willing to go with VOR/DME. The Navy placed both a VOR/DME and a
TACAN aboard a ship and demonstrated that the TACAN would operate around the
superstructure of a ship with far lass degradation than the VOR portion of a
VOR/DME. Thus, for that reason the military went with TACAN.

So, we ended up with all these duplicate civil facilities (VORTACs) to satisfy a
Navy requirement at sea.