But then, the questions are how a diesel submarine is propelled and how long can it stay submerged under water? Most diesel submarines are equipped with two or more diesel engines. The diesel engines can power propellers or generators that recharge a large battery bank. They can also be used in combination with one driving a propeller and a generator. To use the diesel engines, the submarine may surface (or travel slightly below the surface using a snorkel). Meanwhile, the sub can go underwater after the batteries are fully charged.