Capital ship The capital ships of a navy are its most important warships ; they generally possess the heaviest firepower and armor and are traditionally much larger than other naval vessels . A capital ship is generally a leading or a primary ship in a naval fleet . There is usually no formal criterion for the classification , but it is a useful concept in naval strategy ; for example , it permits comparisons between relative naval strengths in a theatre of operations without the need for considering specific details of tonnage or gun diameters . A notable example of this is the Mahanian doctrine , which was applied in the planning of the defence of Singapore in World War II , where the Royal Navy had to decide the allocation of their battleships and battlecruisers between the Atlantic and Pacific theatres . The Mahanian doctrine was also applied by the Imperial Japanese Navy , leading to their preventive move to attack Pearl Harbor and the battleships of the U . S . Pacific Fleet . The naval nature of the Pacific Theater of Operations , more commonly referred to as the Pacific War , necessitated the United States Navy to deploy its battleships and aircraft carriers in the Pacific . The war in Europe was primarily a land war , consequently , Germany ' s surface fleet was small , and the escort ships used in the Second Battle of the Atlantic were mostly destroyer s and destroyer escort s to counter the U - boat threat . Era of sail . Before the advent of the all - steel navy in the late 19th century , a capital ship was generally understood as a ship that conformed to the Royal Navy ' s rating system of a ship of the line as being of the first , second , third or fourth rates : Frigate s were ships of the fifth rate ; sixth rate s comprised small frigates and corvette s . Towards the end of the Napoleonic Wars and into the late 19th century some larger and more powerful frigates were classified as fourth rates . Battleship / Battlecruiser . The definition of " capital ship " was formalized in the limitation treaties of the 1920s and 30s in the Washington Naval Treaty , London Naval Treaty , and Second London Naval Treaty . This applied mainly to ships resulting from the dreadnought revolution ; dreadnought battleships ( also known first as dreadnoughts and later as battleships ) and battlecruisers . In the 20th century , especially in World Wars I and II , typical capital ships would be battleship s and battlecruiser s . All of the above ships were close to 20 , 000 tons displacement or heavier , with large caliber guns and heavy armor protection . Heavy cruiser s , despite being important ships , were not considered capital ships . An exception to the above in World War II was the . Though this class was technically similar to a heavy cruiser , albeit with considerably heavier guns , they were regarded by some as capital ships ( hence the British label " Pocket battleship " ) since they were one of the few heavy surface units of the Kriegsmarine . The s , despite being oversized heavy cruisers and not true battleships / battlecruisers , were also considered by some to be capital ships . During the Cold War , a Soviet large missile cruiser had a displacement great enough to rival WWII - era battleships and battlecruisers , perhaps defining a new capital ship for that era . Regarded technical design , however , the " Kirov " is just a supersized guided - missile cruiser with nuclear propulsion . Aircraft carrier . It took until late 1942 before aircraft carrier s were universally considered capital ships . The U . S . Navy was forced to rely primarily on their aircraft carriers after the attack on Pearl Harbor sank or damaged eight of their Pacific Fleet battleships . In the 21st century , the aircraft carrier is the last remaining capital ship , with capability defined in decks available and aircraft per deck , rather than in guns and caliber s . The United States possesses supremacy , in both categories of aircraft carriers , possessing not only 10 active duty supercarrier s each capable of carrying and launching nearly 100 tactical aircraft , but an additional 12 amphibious assault ship s as capable ( in the " Sea Control Ship " configuration ) as the light VSTOL carriers of other nations . Desipte their significance to modern fleets , the US Navy has never named aircraft carriers after US states as was the practice when battleships ( e . g . Iowa class ) were considered capital ships . Instead US state names are today applied to nuclear submarines indicating that they are considered superordinate to aircraft carriers in the current hiearchy of US ship types . Nuclear Submarines . Ballistic missile submarine s ( or " boomers " ) , while important ships and similar in tonnage to early battleships , are usually counted as part of a nation ' s nuclear deterrent force and do not share the sea control mission of traditional capital ships . Never - the - less many navies , including the Royal Navy and the United States Navy , consider these ships to be capital ships . Beginning with the first class of Trident equipped ballistic missile submarines ( i . e . the Ohio class ) state names have been applied to US nuclear submarines indicating their status as capital ships . Previous ballistic missile submarines ( e . g . Poseidon missile equipped submarines ) had not been named for states . After the completion of the last Ohio class ballistic missile submarine , state names were applied to attack submarine s ( e . g . Virginia class ) . Earlier attack submarines had been named for major cities ( e . g . Los Angeles class ) - as was previously the practice for cruisers ( e . g . USS Indianapolis ) Naming . Some navies reserve specific names for their capital ships . Names reserved for capital ships include chiefs of state ( e . g . ) , important places ( e . g . ) , historically important naval officers or admiralty ( e . g . ) , historical events or objects ( e . g . ) , traditional names ( e . g . ) . However there are some exceptions to the rule . Beginning with the USS Texas ( BB - 1 ) ( the first US battleship ) , US capital ships have traditionally been named after US states . Lesser vessels are named after US territories ( e . g . Alaska class battlecruisers ) , major US cities ( e . g . crusier s ) , or US presidents ( e . g . early attack submarine s and late aircraft carriers ) . Prior to and during WWII the Imperial Japanese Navy also followed the practice of naming battleships after provinces ( e . g . IJN Yamato ) . Beginning with the Ohio class , US state names were applied to ballistic missile submarines indicating their rising status as capital ships equipped with a complement of dooms - day nuclear weapons . After the last delivery of Ohio class ballistic missile submarines , the US Navy began applying state names to attack submarine s ( e . g . the Virginia class ) . In fiction . The term has been adopted into science fiction literature and culture to describe large spaceships used in military contexts , particularly where other naval terms have also been adopted in similar fashion ; for example , sci - fi capital spaceships are often " carriers " , that carry small fighters analogous to the way the real - world naval equivalent carries fighter aircraft , as well as functioning as " battleships " .