SUBMARINES
A submarine is a vessel that can travel submerged under the water as well as on the surface. A submarine needs an extremely strong hull to resist the pressure deep under water. Ballast tanks in the hull are filled with water to make the submarine heavier so that it dives. The tanks are “blown” with air to empty them and make the submarine surface again.
While submerged, submarines are propelled by battery-powered electric motors that do not produce dangerous exhaust fumes. On the surface, diesel engines take over. They recharge the batteries at the same time.
Huge military submarines such as USS George Washington lurk under the water and attack enemy ships with torpedoes. Nuclear-powered submarines can stay submerged for months.
A submersible such as Alvin is a miniature submarine. Submersibles are mostly used for research in the ocean depths. Robot submersibles also carry out underwater repairs on oil rigs.
Picture Credit : Google