Timothy P. Mulligan's Neither Sharks Nor Wolves is an academic study of U-Boat crews of WWII, published by Naval Institute Press in 1999. He describes the rank structure of the officers as:
- Commander: ranked as Kapitänleutnant, or Oberleutnant zur See.
- 1st Watch Officer: Oberleutnant zur See or Leutnant zur See.
- 2nd Watch Officer: Leutnant zur See.
- Chief Engineer: Oberleutnant [Ing.]
The 1st Watch Officer was the second-in-command. Where Mulligan gives two possible ranks, the higher rank would be for more experienced officers, with a slight bias towards them commanding larger boats.
In addition, there could be a commanding officer in training, presumably an officer who hadn't served in submarines before who was converting to the work, or a medical officer. There would also be one or two apprentice officers, Fähnrich zur See, but Mulligan groups them with the seaman senior NCOs.