Re: found what I believe are a few vrc drum pickup heads too bad photos don't post here interested parties,can email

[Chuck Guzis via cctalk]

My guess was MADRE or NRL:

https://www.wikiwand.com/en/Over-the-horizon_radar

The timing would be right.  Acoustic delay lines served the same
purpose, but you couldn't have a mercury delay line in an airplane,
practically speaking.

--Chuck