FYI Karl-Arne's done some research on air to ship comms following a question on Thursday night:
-------- Forwarded Message --------
Subject: Sv: Sv: meeting Thursday 11th May: Stockholm Radio (STORADIO) aero HF station by Karl-Arne SM0AOM zoom info - THANKYOU!!
Date: Sun, 14 May 2023 11:09:00 +0000
A quite interesting question was raised after my presentation;
about the interoperability between aircraft and ship stations,
especially when using crystal-controlled equipment.
I remember from my earliest years in the business that this sometimes
was discussed, but that it was considered a "minor issue", as quite few
HF aircraft equipments reliably covered frequencies where regular listening watches
The 1 kHz channelised SSB transceivers (mid-60s onwards) usually were not specified to operate
lower than about 2.4 MHz due to antenna matching issues, which made calling on 2182 kHz impractical, especially from small aircraft and helicopters.
Some archive research of ITU, ICAO, STC, Collins and ARINC documentation netted these results:
In the 1947 Radio Regulations there were "preferred calling frequencies" for Morse
in all primary HF Maritime Mobile bands which also were permitted for aircraft use.
Also, aircraft flying in oceanic airspace were required to be able to communicate on 500 kHz if Morse capable and on 2182 kHz as well as on the aero HF frequencies.
Most pre-SSB equipment (Collins 18S and 618S) went down to 2 MHz.
Then the world-wide aero "coordination" frequencies of 3023.5 and 5680 kHz also were available.
So it can be assumed that a 40s/50s aircraft that wanted to establish contacts with
ships along an oceanic route used some form of scheduled appointments where the ship stations in range were called on pre-arranged frequencies and times either on 500/4182/6273/8364 kHz Morse or using AM telephony on 2182/3023/5680 kHz.
It would however take special arrangements for arranging schedules with "ordinary" ship stations, so it would in practice have been confined to i.e. "weather ships" and their likes.
This may also have presented a problem with the oldest channelised aircraft HF transceivers that only had 12 or 24 crystal positions, but became more managable with the later ones which had 100 (STC STR18) or 144 positions (Collins 618S).
You can share this with the questioner.