Dear Sirs,
my question comes also from the U-505 capture. I have read all the relevant information on this site. That boat came off nearly scuttled, low both on compressed air and stored amperes. One crewman, a Polish national drafted into the Kriegsmarine, actually gave directions to the American engineer and prize crew about how to operate her. After stopping the sinking they pumped out, by external means, most of the unwanted saltwater, then they towed the U-boat with the jammed rudder. This operation proved to be an headache, so they had to fix the rudder. Still under tow, they recharged the accumulators through the "windmilling" propellers turning the motor-generators. According to the answers to my question, most likely those amperes were used to get compressed air turning one air compressor by the electric engine. Then they started the Diesel engine(s) and the boat could sail under his own power. Anyway I still presume that one U-boat electric motor had enough torque to start the Diesel directly but maybe I am wrong.
Greetings and thanks.
walter M