You have described the propulsion system on the Wilhelm Bauer after she was rebuilt in 1959 with two 2,000 HP Diesel generating sets. The propulsion system on U-2540 was different and rather similar to the VII/IX set up with the main difference being the two 113 HP creep motors which were connected to the drive shafts by a bunch of V-belts. The XXI was a true Diesel-electric boat only up to 6 knots which was the maximum speed it could do using the creep motors. The two main electric motors would be operating in generator mode at this time. At higher speeds, the propulsion system was the same as the VII/IX.

The type XXIII had a similar arrangement as the XXI with one 580 HP Diesel, one 580 HP electric motor/generator and a 35 HP creep motor.

Regards,
SuperKraut