How long could these boats remain submerged during WW2?
The record during the war was just short of 38 hours by the USS Puffer (SS-268). She was a Gato class boat built by Manitowoc Shipbuilding. She was being tracked and depth charged by Japanese ASW vessels. At 38 hours, the battery was nearly discharged and oxygen was low. The captain decided his choices were to either suffocate submerged or take a chance on surfacing and fighting it out with the Japanese ships. He chose to surface. The boat was fortunate in that the currents had carried it a few miles away from the hunters. The captain then presented the stern to the hunters, so it showed the smallest profile. He was able to use an island as a backdrop to make the boat even harder to see. The boat was then able to make repairs and escape back to base.
That was the longest submergence during the war and very unusual. Normally, these boats would be on the surface each night. They wanted to recharge the battery, get fresh air in the boat, get a star fix and pick out their messages from the fleet broadcast. The air in the boat was the same air the crew had been breathing since they submerged. It was expected to last 16 to 18 hours. (Since most of the crew smoked cigarettes, we will call that 16 hours.)
There were some things that could be done to extend the air. There were five or six oxygen bottles on board. There were also multiple cans of CO2 absorbent in the overheads. (Those were the cans labeled “DO NOT PAINT”.) The oxygen and CO2 absorbent would extend the air a few hours. After that, they would bleed some high-pressure air into the boat. It wasn’t fresh air, but it improved the percentages and sustained life.
But air wasn’t the only issue. The other was battery power. How long the battery could last depended on how fast the boat was going. The battery was rated at 48 hours if the boat was going two knots. However, if they doubled the speed to four knots, they had to divide the time the battery would last by eight. It was a cubic relationship. At four knots the battery would last about six hours. Double it again to eight knots, nearly the maximum speed the boat could go submerged, and the battery would last less than one hour. It was called the “one-hour rate”.
Clearly, it was important to use the battery and air conservatively when the boat was being attacked. Slow and silent was the best way to conserve the battery and to escape. To use air more efficiently, put all non-essential crewmen in their bunks. They used less oxygen when resting.