SSN (hull classification symbol)

The first nuclear-powered attack submarine was the US Navy's USS Nautilus, operational from 1954. This was followed by the four submarines of the Skate class entering service in 1957. The Royal Navy's first nuclear fleet submarine was HMS Dreadnought which by using an American reactor entered service in 1963. The first all-British nuclear submarines were the two Valiant-class submarines.

The USN submarine fleet has been all-nuclear powered for over two decades. The last Barbel-class diesel-electric attack submarine, USS Blueback (SS-581), was decommissioned in 1990. The bulk of the USN's SSN fleet has been the Los Angeles-class attack submarine. Designed during the Cold War the Los Angeles-class boats' raison d'etre was to protect USN carrier battle groups and to hunt Soviet Navy SSBNs before they could launch a first strike against the United States.

The first ever major combat action involving an SSN was during the 1982 Falklands War. An Argentinian cruiser, ARA General Belgrano was sunk by torpedoes fired by the Royal Navy fleet submarine HMS Conqueror. After that incident, the Argentinian Navy was effectively confined to port.

Since the end of the Cold War, SSNs have evolved into multi-mission submarines. Their roles include submarine-launched cruise missile platforms, intelligence gathering platforms, insertion and exfiltration of special forces teams in addition to traditional hunter-killer SSN roles.

The advantages of an SSN over a conventionally powered SSK are much longer endurance (limited more by the crew than the boat, a nuclear submarine can stay submerged for months and does not need refueling in their 25-year lifespans), and higher speed. Unlike most SSKs, SSNs do not have to surface periodically for air, which would compromise their stealth. Some of the newest conventional submarines approach these advantages: Stirling engine powered vessels can cruise underwater for up to two weeks and, like diesel/electric vessels (and in theory LOX powered vessels), are significantly quieter than nuclear submarines, since they do not need to run the powerful (and noisy) pumps associated with the cooling circuits of pressurized water reactors.

The main disadvantages of an SSN are the technological challenges and expenses of building and maintaining a nuclear power plant. Nuclear submarines can have political downsides, as some countries refuse to accept nuclear-powered vessels as a matter of policy. Furthermore, decommissioned nuclear submarines require costly dismantling and long term storage of the radioactive waste.

The following navies currently operate SSNs:

• People's Liberation Army Navy of China
• French Navy
• Indian Navy
• Russian Navy
• Royal Navy of the United Kingdom
• United States Navy

  Royal Australian Navy

• Virginia-class submarine – three planned (with an option to purchase a further two vessels)
• SSN-AUKUS – up to eight planned

  Brazilian Navy

• Brazilian submarine Álvaro Alberto – one under construction^[3][4][5]

  People's Liberation Army Navy of the People's Republic of China

• Han-class submarine (Type 091) – three in service, two retired
• Type 093 submarine – six in service
• Type 095 submarine – five planned ^[6][7]

  French Navy

• Rubis-class submarine – four in service, two retired
• Barracuda-class submarine – one in service, second on sea trials, total of six planned

  Indian Navy

• Akula-class submarine – one to be delivered by 2025.^[8] (Another leased Akula class submarine was returned to Russia in 2021, before the end of its contract.^[9][10][11] )
• Project 75 Alpha – 2 cleared,^[12] 6 planned ^[13][14]

  Russian Navy

• Victor III-class submarine – three in service, 45 retired
• Sierra II-class submarine – two in service
• Akula-class submarine – 10 in service, four retired
• Yasen-class submarine – three in service, one on sea trials, total of 12 planned

  Royal Navy of the United Kingdom

(Known as "fleet submarines" in the Royal Navy.)

• Trafalgar-class submarine – one in service, six retired
• Astute-class submarine – five in service, two more under construction
• SSN-AUKUS – number TBD (first design contract awarded)

  United States Navy

• Los Angeles-class submarine – 30 in service, 32 retired
• Seawolf-class submarine – three in service
• Virginia-class submarine – 19 in service, 66 planned in total
• SSN(X)-class submarine – number TBD (under development)

  Indian Navy

• INS Chakra (1987) was formerly the Charlie-class submarine K-43 leased in 1987 from Russia and returned in 1991. ^[15][16]
• INS Chakra (2011) was formerly the Akula-class submarine Nerpa leased from Russia in 2011 and returned in June 2021.

  Royal Navy of the United Kingdom

• HMS Dreadnought - the Royal Navy's first nuclear-powered fleet submarine 1963 - 1980
• Valiant-class submarine - 2 submarines in service 1966 - 1994
• Churchill-class submarine - 3 submarines in service 1970 - 1992
• Swiftsure-class submarine - 6 submarines 1973-2010

  Soviet /   Russian Navy

• November-class submarine 1958-1991
• K-278 Komsomolets - only member of the "Mike" class, 1984 - 1989 (sank after fire)
• Alfa-class submarine

  United States Navy

• USS Nautilus��(SSN-571) (unique)
• USS Seawolf (SSN-575) (unique)
• Skate-class submarine - 4 submarines in service 1957 - 1989
• Skipjack-class submarine - 6 submarines in service 1959 - 1990 (One lost, 1968)
• USS Triton (SSN-586) (unique)
• USS Halibut (SSN-587) (unique)
• Permit-class submarine - 14 submarines in service 1961 - 1996 (One lost, 1963)
• USS Tullibee (SSN-597) (unique)
• Sturgeon-class submarine - 37 submarines in service 1967 - 2004
• USS Narwhal (SSN-671) (unique)
• USS Glenard P. Lipscomb (SSN-685) (unique)

• Nuclear submarine
• Ballistic missile submarine (SSB/SSBN)
• Cruise missile submarine (SSG/SSGN)
• List of submarine classes
• List of submarine classes of the Royal Navy
• List of Soviet and Russian submarine classes
• List of submarine classes of the United States Navy