About 2,100 by many different countries.
Both sides, the Allies and the Axis, had submarines when WW2 started.
Yes
They were much smaller in World War II. Even the crews quarters where cramped. The air exchange and diesel fumes, along with the batteries, made it dangerous and rough.
During World War 2, it is reported that over 2,000 variants of Japanese Submarines were used during World War 2. Out of this, it is estimated that 10,000s were likely to be used during WW2.
326
Underseaboats.U-boats
Wolfpack
The British lost 76 submarines during WWII.
Underseaboats.U-boats
52
759
9