You're probably thinking of U-Boats. It MIGHT apply to the S boat on the surface - I never did a full study of it, but I recall reading somewhere that the 1918 armistice surrendered a bunch of different U-Boats to various allied forces. The S boat was allegedly based on a 1915 U-Boat design which had a priority that it could be built quickly and cheaply, with all the compromises that go along with that. In other words the design was so bad the Germans didn't really want it, they needed it because they were running out of time and materials.
Best I recall WWII German, British, and all US boats up until the Porpoise class were direct drive, the Porpoise was the first diesel-electric design which used the electric motors at all times, with the diesels coupled to generators so all they ever did was create electricity for running the motors and charging the batteries. The direct drives came in several flavors, most had the motor-generator core wrapped around the propeller shaft so when the field control current was off, it was nothing more than a big copper flywheel. Turn one field circuit on and it became a motor, turn the other one on and it became a generator. The diesels had a clutch which could be disengaged, and most were designed without any kind of transmission, instead they had to be shut down and started in reverse to back up. If there was power in the batteries there was no real need for that since you could just throw out the clutch and back with the motors. Other designs had the motor-generator separate from the shaft with gears and sometimes clutches, but best I recall the U-Boats had to run at 9 knots minimum to charge the batteries. Which made snorkeling a real beast. Once they got the bugs out of it the diesel-electric was a much better design.
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