How long can a WW2 U-Boat stay underwater?

WWII submarines making a journey of any length would run on diesels on the surface during the day, if there were reasonable odds of not being sighted. Rapid ("crash") diving was a very important tactic for them, and the ability to do it quickly was an important factor in both sub design and crew training. read more

The U boat was just that. A small ship with the capability to travel underwater for a limited time, not a true submarine. On the surface, the boats were powered by two diesel engines turning both screws and generators which charged the large bank of lead-acid batteries. read more

A German type VII U-boat could stay submerged for about 24 hours before it had to resurface to replenish its air supply. This air supply could be extended somewhat by limiting activities of the crew while submerged. The type IX could stay submerged for 11 days. The snorkel in 1943 allowed German subs to stay submerged and refresh air. read more

It may have to stay down longer than 12 hours if some ship happen to be nearby. I'm interested in subs of Japan, Germany, Russia, Britain, and America. Edit: I should have specified this, but I want to know how long the sub can stay down near max depth, not snorkeling. read more