In the early days, long-term Notices to Airmen (NOTAMs) were published in hard copy form as 'Series B' NOTAMs. After the Second World War these became known as 'Class II' NOTAMs, and later as 'AIP Supplements'.
The example NOTAM below, number 6/1940, lists the callsigns of Australian Aeradio Stations. This NOTAM introduced a change to the first two letters of station callsigns to 'VZ'. They were previously 'VH', which obviously presented the possibility of confusion with aircraft registrations. Coastal Radio Stations operated by AWA, used by aircraft where there was no Aeradio Station, continued to use three-letter callsigns.
Note that almost all communications at that time were done by Morse Code rather than by voice. Also, the Flying Boat Bases established in 1938 to support the Empire Air Mail Scheme have two allocated callsigns: one for the Aeradio Station itself and another for the radio-equipped Control Launch. Control Launch callsigns all ended in 'Z'. For example, Karumba Aeradio's callsign was VZKA whereas the Karumba Control Launch had the callsign VZKZ.
(NOTAM: CAHS collection)
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