How Does a Submarine Engine Work Underwater?

Underwater, a submarine primarily relies on electric motors powered by batteries for propulsion, as its diesel engines require access to air.

Traditional diesel-electric submarines cannot run their diesel engines when fully submerged because these engines need oxygen to operate. Therefore, a different system is used for underwater travel.

Powering the Submerged Submarine

Here's how a diesel-electric submarine typically operates and gets power underwater, according to the provided information:

• Diesel Engine Use: The diesel engines are primarily used when the submarine is on the surface or cruising just below the surface using a snorkel. This allows the engines to draw fresh air from above the water.
• Battery Charging: While operating on the surface or snorkeling, the main purpose of the diesel engines is often to generate electricity to recharge the submarine's large bank of batteries.
• Underwater Operation: Once the batteries are fully charged, the sub can head underwater. The batteries power electric motors that drive the propellers.
• Submerging Power: The reference explicitly states: Battery operation is the only way a diesel sub can actually submerge. This highlights that the power source for fully submerged propulsion comes from the batteries driving the electric motors, not the diesel engines.

Think of it like a hybrid car: the diesel engine (like a gasoline engine) is used for charging or surface cruising, while the electric motor provides silent power for submerged travel.

In summary, while the submarine has diesel "engines," the system that works underwater for propulsion is the combination of large batteries discharging power to quiet electric motors. The diesel engines are essential for recharging the batteries when the submarine has access to air.