Commercial air mail cover from BASSEL(SWITZERLAND) to ISTANBUL (TURKEY) . Postmarked with ‘BASSEL ST JOHANN * 14 VII 45’.

On its way to SWEDEN passed from LONDON (which functioning as first exchange office for the forwarding to the second), where hand stamped with the red rubber air mail marking O.A.T. [Onward Air Transmission]. After examining contents (censorship) was closed with resealing tape texted ‘OPENED BY EXAMINER 4059 (type P.C.90)'

The place these marking was used is not shown because the reason of their existence was to facilitate the transfer of the mail by supplying information from one postal administration to another, as imposed from U.P.U. for the categories of postal articles.

Note: There are at least 15 types of air mail markings O.A.T.