As a signatory of South East Asia Treaty Organisation (SEATO), Britain had an obligation to assist Allies in the Far East.
In early 1960’s, the Americans (also a signatory to SEATO) were becoming increasingly embroiled in preventing the march of Communism in Laos and Vietnam, they requested that Britain assist in their crusade.

In February 1963, it was proposed that Britain construct an Airfield at Loeng Nok Tha, near Mukdahan in Thailand, as part of the American’s Special Logistic Aid to Thailand (SLAT).
The proposal was accepted and given the code name “Operation Crown”.

These Units were involved in the construction of that airfield:

11 Independant Field Squadron RE
34 Field Squadron RE
59 Field Squadron RE
54 Corps Field Park Squadron RE - Detachment
84 Survey Squadron RE - Detachment
302 Postal Unit RE - Detachment
2 Plant Trp, 2 Construction Sqn Royal New Zealand Engineers
2 Troop of 7 Field Sqn, Royal Australian Engineers
5001 RAF Airfield Construction Unit
ACC,
16th Commonwealth Field Ambulance RAMC,
RAOC ,
RASC (RCT) + 6 RA Drivers
REME,

(appologies for any units missed from this list)

Operation Crown

The airfield with its 5,000ft long air strip, control-tower, airfield fencing and lighting was completed in time for an official opening ceremony on 17 June 1965, but work continued on improving the landing strips long after the ceremony.

After the airfield was completed a second project, to build a road north west from Loeng Nok Tha to a village (Ban Khok Klang), was started in December 1966 by 34 Field Squadron RE, who were relieved by 59 Field Squadron RE in August 1967, who in turn were relieved by 11 Field Squadron RE. The road was completed in April 1968 by a composite workforce that included:

54 (FARELF) Support Squadron RE
51 (Airfields) Squadron RE - one troop
59 Field Squadron RE - one troop

The initial project was continually extended with add on projects and there was a continued presence of British forces in Thailand from 1963 to 1971.

A Royal Engineers' Forces Post Office attached to the British Embassy remained in Bangkok after the last of the Royal Engineers involved in Operation Crown departed Thailand in 1968.