GSM with Vietnam Clasp seem to have been Australian personnel onlyâ€¦
This clasp was instituted by Royal Warrant dated 8 June 1968 for award to Australian personnel. Only 68 clasps were issued, and all 68 went to members of the Australian Army Training Team.
The various qualifying periods, between 24 December 1962 and 29 May 1964, were
30 days' service in ships operating in inland waters or off the Vietnamese coast.
1 day in the service of a land unit.
1 operational sortie.
30 days' service on an official visit.
For service after 29 May 1964, the personnel were awarded The Australian Vietnam Medal.
Rumour at the time, and its is only a rumour that I heard was that any RN service personal who MOD wanted to serve in Vietnam be they Divers and they are the ones to whom the rumour I heard was about, or any others were transferred on paper to the RAN for the time on Station.