I've read the articles of the links above and one thing I wasn't aware of became clear to me. The diesels are not connected to the propeller shafts, but driving them through the electric engines. That's fine. I was a little surprised, though, as this means that there would be no propulsion, not even on the surface, if the e-engines were damaged. I suppose this was done to save space and weight.

OTH, it doesn't seem clear to me whether the propeller shaft/propellers could be disconnected from the engines or not. A gearbox. Or maybe adjustable propeller pitch. To me it sounds unlikely that batteries couldn't be charged while lying still. Since the e-engines themselves were the battery charging generators, driven by the diesels, the axles would then swirl while charging. This would also take up/diminish energy for the actual charging. And the boat would move.

Can anyone point specifically to a source which says this.

That, I believe, is not the essence of the links above. They say that all propulsion goes through the e-engines. That is, the diesels are not coupled to the axles. Whether that is correct or not I do not know. But that is how I understand the information in the links. That said, and if it is correct, I find it strange if there is not a sort of (de)coupling between the e-engines and the axles/propellers as the e-engine as a generator for charging needs to revolve. Modern u-boats might have a different system.

If you think about it from the diesels' point of view such a propulsion system is advantageous in that these can be run on near constant speeds instead of suffering from the various stress loadings caused by the variation of stress on the propeller and axles which supplants to the diesels.

So, when under speed, and charging, one diesel would drive the e-engine driving one axle/propeller while the other diesel drives the e-engine as a battery generator (which, on low speed, also can give propulsion power to the other axle/propeller while charging) - or - one diesel drives both the propulsion e-engine and the one charging.

As a commander I would certainly have liked to have the possibility to lie still on station while charging. After all, keeping station was a major part of the game - when you first got there. Any other solution i'd say would be very inflexible. Not to say that it wasn't like that. I do no not know but I would like to find out about this.

I should think so, but you got to go up and charge eventually. So, should you stay in the same location or let yourself be "driven" while doing so. Another thing, while we're on recharging. Wouldn't the recharging give off more sounds if the propellers were rotating. What is easier to detect - the vibrations from the diesels or the propellers moving....I don't know....

Hmmm, would that charge the batteries....?....I suppose it would if the axles/propellers weren't disconnected.....if they could be disconnected....if they couldn't it would be heavier to row....boy, that's a serious drawback....better than rigging a sail - a windmill. That could charge the batteries....:hmmm:....hmm...we are getting somewhere now...