Bruce,

Very interesting story. I have not reviewed the KTBs of all Constaninople-based U-boats to specifically rule out that they were ever in the area, but I find it extremely fanciful.

Some points:

• The Germans had a perfectly good base at Constaninople.
• The war diaries of WWI U-boats survive; copies on microfilm are available from the U.S. National Archives and Records Administation.
• A number of small U-boats were based at Constaninople (UBI and UCI classes), however, these were used virtually exclusively in the Black Sea against the Russians.
• Constinople also had a three UBIIs and two UCIIs based there. After arriving in Constaninople, UB 45 and UB 46 were used exclusively in the Black Sea until sunk. UB 42 was in the Black Sea in 1916 and then did four four patrols in the Aegean or Eastern Med in 1917.
• UC 37 didn't arrive in Constaninople until July 1918
• UC 23 arrived in Constaninople in December 1916 and operated extensively in the Aegean Sea. She was also a minelayer with good torpedo attack capacity. The secondary accounts have all her patrols beginning and ending in Constaninople.
• U 21, U 33, and U 38 all were in Constaninople at one time or another. In the case of U 33 and U 38, this was in 1916 -- to operate against the Russians in the Black Sea (the Russians staged a major offensive in 1916 in the Caucasus).
• The Turks had no operational submarines.

Best wishes,

Michael