High Quality Content by WIKIPEDIA articles! The capital ships of a navy are its most important warships; the ones with the heaviest firepower and armor. A capital ship is generally a leading or a primary ship in a fleet. There is usually no formal criterion for the classification, but it is a useful concept when thinking about strategy, for instance to compare relative naval strengths in a theatre of operations without having to get bogged down in the details of tonnage and gun diameters. A good example of this is the Mahanian doctrine, which was applied in the planning of the defence of Singapore in WWII, where 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 which led to their pre-emptive move to attack Pearl Harbor and the US Pacific battleships.