Thailand. (Domestic Air Mail Service). 1925. Air Mail envelope addressed to Bangkok bearing Siam SG 231, 3s chocolate, SG 232, 5s green and SG 234, 15s carmine tied by small 'aeroplane' date stamp of UBOL dated '17.3.23' (date error 23 for 25) and small aeroplane arrival of Bangkok/ 10 on reverse '20.3.25'.
Carried on the weekly flight of the Royal Aeronautical Service from Ubol to Bangkok.