Question on Sonderstaffel Tr.O.

[Seaplanes]

The Sonderstaffel Tr.O. (Transozean) was one single Staffel operating the Dornier Do 26 aircraft and also one or two Blohm & Voss Ha 139. The letters you refer to are the individual aircraft letters. The unit code was P5+ -H. The individual letters were A,B,C,D and on. However, only 6 Do 26 were ever built, three being lost during the campaign in Norway (then with 9./K.G.z.b.V. 108 but flown with marking of Sonderst. Tr.O) and one in November 1940 in Brest.