chall

The 27 Mhz theory sounds the most plausible. Those crystals are clearly labelled, and that would explain the sailors. I think a lot of sailors use 27 Mhz because their radio needs are so modest compared to aircraft. (They think 2 channels is a lot.)

If I can find a definitive answer to this from an authoritative source I will come back and post it here.

Thanks for the input so far.