Submarine

Submarine vessels differ from ships because they can travel beneath the surface. Military submarines patrol oceans for weeks, while scientific submersibles study deep-sea ecosystems. Strong pressure hulls made of steel or titanium protect crew from crushing water pressure.

To dive, submarines flood ballast tanks with seawater, increasing weight so the craft sinks. To surface, compressed air forces water out of the tanks, making the submarine buoyant again. Propellers or pump-jet systems push the submarine forward, and hydroplanes steer it up or down.

Modern nuclear submarines use reactors that generate heat for turbines, allowing them to operate for months without refueling. Diesel-electric submarines run on batteries underwater and recharge at the surface. Sensors such as sonar, periscopes, radar, and satellite links help crews navigate and communicate discreetly.

Scientific submersibles carry cameras, robotic arms, and sampling gear to explore hydrothermal vents, shipwrecks, and deep trenches. Autonomous underwater vehicles (AUVs) operate without crews, mapping the seafloor and monitoring pipelines.

Safety features include escape trunks, emergency breathing systems, and rigorous training. International agreements regulate submarine operations to prevent collisions and protect research sites.