The doc i refer to, seems official. I maybe will attach it in a later email.

I have to opine "They were NOT much used". I had one of last ATBs sold by G&G, must have been about ? 1980 ?   I sold it, with 'pilot's control box' around 2014. I still have one ATB, gotten from a wartime PBY pilot, but i need to find the keying relay, which was removed by him, but which i still have.

I do remember, "Never say never."

-Hue Miller