a battleship. By the early 20th century, cruisers could be placed on a consistent scale of warship size, smaller than a battleship but larger than a destroyer. In 1922, the Washington Naval Treaty placed a formal limit on cruisers, which were defined as warships of up to 10,000 tons displacement carrying guns no larger than 8 inches in calibre. These limits shaped cruisers until the end of World War II. The very large battlecruisers of the World War I era were now classified, along with battleships, as capital ships. In the later 20th century, the obsolescence of the battleship left the cruiser as the largest and most powerful surface combatant (excluding aircraft carriers). The role of the cruiser varied according to ship and navy, often including air defense, commerce raiding, and shore bombardment. The U.S. Navy in the Cold War period built guided-missile cruisers primarily designed to provide air defense, while the navy of the USSR built battlecruisers with heavy anti-ship missiles designed to sink NATO carrier task forces. (27 completed; 22 in active service, 5 retired) – the first ship class with the AEGIS combat system Destroyers Destroyers DDG are fast maneuverable long-endurance warships intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller powerful short-range attackers. They were originally developed in the late 19th century as a defense against torpedo boats, and by the time of the Russo-Japanese War in 1904, these "torpedo boat destroyers" (TBD) were "large, swift, and powerfully armed torpedo boats designed to destroy other torpedo boats." Before World War II, destroyers were light vessels with little endurance for unattended ocean operations; typically a number of destroyers and a single destroyer tender operated together. After the war, the advent of the guided missile allowed destroyers to take on the surface combatant roles previously filled by battleships and cruisers. This resulted in larger and more powerful guided missile destroyers more capable of independent operation. At the start of the 21st century, destroyers are the heaviest surface combatant ships in general use, with only two nations (United States and Russia) currently operating the heavier class cruisers, with no battleships or true battlecruisers remaining. Modern destroyers, also known as guided missile destroyers, are equivalent in tonnage but vastly superior in firepower to cruisers of the World War II era, capable of carrying nuclear tipped cruise missiles. Guided missile destroyers such as