Franz was Crew 26 & was promoted to Kapitänleutnant 1 April, 1936. He was promoted to Korvettenkapitän 1 April, 1941.

Glattes was Crew 27 & was promoted to Kapitänleutnant 1 October, 1936. He was promoted to Korvettenkapitän 1 September, 1941.

In 1939 they were both Kapitänleutnant and there is no rank between Kapitänleutnant & Korvettenkapitän so Franz would have been the senior of the two.

Both U-boats normally had 4 officers:
Commander, IWO, IIWO, & LI. The IIIWO was generally a senior Petty Officer (enlisted man, generally the navigator, not an officer).

However they sometimes had officers in training, a doctor on rare occasions, and even passengers on even rarer occasions.

No idea if more than the normal 4 were aboard either boat in 1939
However they sometimes had officers in training, a doctor on rare occasions,

Nothing unusual about officers deferring to a more senior officer. That was how it was supposed to work.

Regards,

Ken Dunn