Commercial cover with Turkish “UÇAK İLE / PAR AVION” airmail facing label from Istanbul, Turkey via London, UK to Switzerland, franked with 5k. effigy of Atatürk (1931-38) + 4k. merino sheep + 1943 2x27½k. effigy of Ismet Inönü adhesives (1943) plus 1941/44 2k. National Defence stamp (surtax) [‘Milli müdafaa pulu’] affixed on reverse; total franking: 65 k. for letter rate + airmail fee, plus the 2 k. surtax.
Stamps cancelled by "YOLCU SALONU 3 / -5-10-45 / 725 GALATA” (Bosphorus Cruise Ships Dock #3 at the Karaköy (Galata) Passenger Terminal, built in 1937); today still as “Yolcu Salonu” on same quays).
The envelope is addressed to firm in Basel, Switzerland as airmail correspondence sent partly by surface means.
It bears a pale red rectangular boxed frame, 31x17mm, and “OAT” with square stops after letters. This "Onward Air Transmission" rubber marking was applied in London, England to indicate that the postage guaranteed air mail transportation beyond to Switzerland.
[OAT markings ("Onward Air Transmission", 1938 to 1974) are recorded used most often from 1940 to 1946 on loose envelopes (especially registered) or only on the top cover of mail in a bundle tied and travelled in open bags. The aim was to indicate the beginning of air transportation from certain exchange offices for the rest of the route, in the same procedure followed in cancelling (defacing) the airmail label for packets going on by surface.
Those applied at London were first oval framed; in 1945 they were smaller and rectangular.]
Condition: Nice; see scans.