In 1620 a Dutchman called Cornelius van Drebben who was living in London at the time constructed two submarines. The second of the two made several successful journeys under the river Thames in Britain. Powered by oars the wooden boat-shaped vessel was made waterproof by oiled leather fitted to all openings, air was supplied by a tube running to the surface. However, it was not until the beginning of the 20th century that technology made submarines practicable and necessary for methods of modern warfare.
An American John. P. Holland was designing petrol engine submarines at the beginning of the 20th century. These submarines had nearly all the basic features of the vessels which fought in World War I and World War II.
Modern submarines rely on diesel engines and electric motors for propulsion. The electric motors are powered by batteries. This limits the time the submarine may remain submerged; it must surface to recharge its batteries. The batteries are recharged by the diesel engines connected to a generator or dynamo.
The nuclear powered submarine does not require batteries and can stay under water almost indefinitely, or at least until food and drink rations for crew run out.
The submarine relies on ballast tanks which when filled with water reduce the vessel's buoyancy causing it to sink. Diving planes alter the trim to move the submarine up or down in the water. To resurface, compressed air is fed into the ballast tanks restoring the vessel's buoyancy and causing it to rise upwards towards the surface. All radio and radar aerials as well as the periscope and snorkel are contained in a structure called the conning tower. The snorkel attachment allows the diesel engines to propel the submarine whilst just beneath the surface. Radar is used to track vessels whilst on the surface and sonar is used when the vessel is submerged.
