Submarines are vessels designed to move underwater. They are capable of independent operations with inbuilt power plants capable of supplying power to the vessel for extended periods. Submarines are different from submersibles which are usually launched from submarines or bigger surface ships and are not capable of operating independently from the mother vessel. Submarines are classed into two types according to their propulsion system; conventional submarines and nuclear powered submarines. The conventional submarines are powered by diesel electric engines and used for a wide variety of applications including for civilian purposes such as research of marine life underwater, laying of communication cables underwater and for military submarines used for coastal defense. Nuclear powered submarines are however exclusively used by the military for open seas patrol because of their unlimited range. These vessels are usually refuelled once every 25 years so their ability to stay submerged for months underwater without surfacing is greatly enhanced. They carry missiles and other offensive weapons and are usually difficult to detect on the open seas. These vessels are usually large with tonnages exceeding 16,000 tons to provide enough space for the missiles they carry and the crew onboard manning the vessel. They are part of a country’s strategic nuclear deterrence force and ensure the survivability of a country’s nuclear weapons in case of an attack. Nuclear submarines are propelled by nuclear reactors which provide heating to water that produces steam needed to propel the vessel. Conventional submarines are usually powered by diesel electric generators that provide propulsion power to the vessel. In newly built submarines, air independent propulsion is now employed for propulsion.