Thailand. (Railway - Penang). 1941. Air Mail envelope hand-stamped 'First Flight Cover/ Per Air Mail' addressed to Penang bearing Siam SG 289, 15s blue tied by bilingual Ban Din Lan ambulant (railway post office) date stamp '6th Aug 84 (41), carried north to Bangkok with circular '3' censor cachet applied in violet with triangular 'Passed For Transmission/ 6' in violet on face on arrival.
Fine item. Ban Din Lan is a railway Post Office in Songkhla Province.