Thailand. (British Force in Thailand). 1965. Air Mail envelope headed 'Forces (Air Mail)' written from 'Plant Troop, Cre Op, Crown, B.F.P.O. 656' addressed to England bearing Great Britain 'Wilding' SG 615, 3d violet tied by 'Field Post Office/ 573' double ring dated '13th April 65'.
Operation "Crown" involved the building of Loeng Nok Tha airfiled in the remote border area of Northern Thailand.
The British had the Field Post Office 573 from '7th Dec 64 - 7th July 1965'.