Why are there so many doorways to go through?

The submarine is divided up into eight compartments on the main level. (The conning tower is a separate compartment above the pressure hull.) These compartments are designed so that if any one of them were to be flooded, the boat could still get back to the surface. (That is a theory that may never have been proven during actual operations.) The compartments are also divided functionally so that noise and light can be suppressed, particularly at night.