Submarines give navies around the world a huge strategic and tactical advantage.
Ballistic missile submarines can serve as nuclear deterrents in case a country's land-based launch systems have been destroyed. Meanwhile, nuclear-powered attack submarines can effectively hunt enemy subs and can sink enemy naval targets. During war games in March, a French Rubis-class sub even "sunk" a US aircraft carrier.
Smaller non-nuclear attack submarines, although incapable of operating underwater for as long as nuclear vessels, can be even more difficult to track than their nuclear-fueled counterparts. These subs can also be used for naval and anti-submarine warfare in shallower waters.
The following graphic from Naval Graphics shows every model of submarine currently in service around the world as of 2015:
On average, the largest submarines in service are ballistic missile-armed. As these submarines are intended for nuclear strikes or long-range missile attacks, few nations have the need or desire to operate them. Today, only Russia, China, the US, the UK, and France have ballistic missile submarines in their navies.
Likewise, the same five countries are the only nations to currently possess nuclear attack submarines, although the Indian Navy is operating a loaned Russian sub. These subs are generally slightly smaller than ballistic missile submarines and are capable of staying submerged for months at a time.
In general, the greatest number of submarines owned and operated around the world are of the non-nuclear variety. These submarines are either powered via air-independent propulsion, diesel-electric engines, or a combination of both.
Although these non-nuclear submarines are small and cannot remain submerged as long as nuclear subs, newer models can potentially run quieter than the nuclear-powered models allowing them to evade detection and attack surface ships or other submarines.
