The submarine is a vehicle capable of carrying out a wide variety of tasks, some of which are unique and multilateral. Consequently, this type of vessel continues to receive special attention of all types of countries, developed or less developed.
Submarines can remain at sea for long periods, requiring only limited logistic support.
They possess high combat strength, in the form of either conventional or nuclear weapons or a combination of both. This fighting capability may either be tactical or strategic i.e., carrying weapons with shorter or longer ranges. Under certain circumstances, the tactical weapons may be used for strategic purposes and some strategic weapons may be equally effective in tactical use. Depending upon the size, these vessels have good staying power at sea, anything from a week to three months for the conventional type and almost unlimited with nuclear propulsion. Nuclear submarines are known to have circum-navigated the earth without refueling, replenishment or putting into any port.