Having looked up U 166 on the \"Boats\" page, seeing as she was lost in 1942 I would hazard a guess that she would not have been fitted with the extended wintergarten up to the point of her sinking as these were not a general fit until 1943. Based upon this supposition ( & I have no evidence to back this up) I would think that armament would be a 20mm on the bandstand and a 30mm on the rear deck.

If someone has more reliable information i would be happy to revise my notes, as accurate info helps everyone.