Walter,
The old XChannel TACAN was equally simple.
1. Switch on.
2. Select T/R for Range and Bearing or Rec for Bearing Only.(Good if you didn't want people to know you were interrogating their beacon).
3. Check Morse ident to confirm you had right beacon.
The range you obtained was accurate to 0.1%. Much better than most radars, at ranges up to around 100nms(ish).
The problem was, sometimes (fairly frequently) the range you got was plain wrong.
No problem when the error was large, because, DR, Mapping Radar and the Omega VLF System would highlight the error.
The problem came on VOR/ LLZR/DME approaches when you were descending
to very low MDA's using step down fixes. An error of 2nms could kill you and your backup aids were not good enough to pick up this small error.
We got around the problem on the C130 by fitting a DME that very rarely did this, and a certified GPS/IN.
Unless the CPLS was 100% foolproof. And like me, you do not seem to know,
the crew had to rely on GPS fed TANS, which they distrusted and switched off, or visual assessment of their DME reading.
There was no fallback to Radar Ranging.