[frau kaleun]

Impossible to say, really - of the vast majority, there is probably no documented record of their personal beliefs and anyone who could bear witness to what those beliefs might have been is long since gone.

Of those who were/are well known, and whose beliefs can be pinned down or guessed at based on documentation or eyewitness reports of what they said and did... at least a couple seem to have been considered "pro-Nazi" in terms of ideology.

How many were "anti-Nazi" to the same degree would probably be more difficult to say based on words and deeds from that time period, since anyone who was would have been less likely to express his opinion about it than someone who wasn't.

I would guess that for the majority, as with the majority of service people everywhere, they were in the service for reasons that had little to do with the government and leaders they ended up serving under, whether they were actively for it or against it. As such they would have been doing their duty as they understood it for whatever government was in power.

Keep in mind that u-boat commanders were commissioned officers, which involved a 25 year commitment to naval service. They didn't get to opt out of the deal based on their personal opinions of who was running the gubmint or what decisions those leaders made. If you were in uniform and the powers that be got you into a war, well, then it was as much a matter of your own survival and the survival of the people you served with and for whom (as an officer) you would be personally responsible once in combat.