If I recall correctly in Das Boot they remained on the bottom for almost 2 days trying to pass through into the Mediterranean before they were finally forced to surface and re-air the boat.
It was not however fun, required special breathing equipment and very few of the men were fighting fit by the end of it.
Since the author of Das Boot says that he personally experienced at the very least similar events to the ones he wrote in the book I would have to guess that a U-boat could probably stay down at least 24 hours, maybe even up to 36.
If the sub was traveling at any speed at all however the battery would give up before the air (judging by Silent Hunter III) in Das Boot they were relying on the Mediterranean currents to carry them through the Gibraltar Straights rather than their engines allowing them to keep the ventialtion running.
__________________
"If all else fails immortality can be obtained by through spectacular error"
John Kenneth Galbroith
|