The battlecruiser, or battle cruiser, was a type of capital ship of the first half of the 20th century. They were similar in size, cost, and armament to battleships, but they generally carried less armour in order to obtain faster speeds. The first battlecruisers were designed in the United Kingdom in the first decade of the century, as a development of the armoured cruiser, at the same time as the dreadnought succeeded the pre-dreadnought battleship. The goal of the design was to outrun any ship with similar armament, and chase down any ship with lesser armament; they were intended to hunt down slower, older armoured cruisers and destroy them with heavy gunfire while avoiding combat with the more powerful but slower battleships. However, as more and more battlecruisers were built, they were increasingly used alongside the better-protected battleships.
Battlecruisers served in the navies of the UK, Germany, the Ottoman Empire, Australia and Japan during World War I, most notably at the Battle of the Falkland Islands and in the several raids and skirmishes in the North Sea which culminated in a pitched fleet battle, the Battle of Jutland. British battlecruisers in particular suffered heavy losses at Jutland, where their light armour made them very vulnerable to large-caliber shells. By the end of the war, capital ship design had developed with battleships becoming faster and battlecruisers becoming more heavily armoured, blurring the distinction between a battlecruiser and a fast battleship. The Washington Naval Treaty, which limited capital ship construction from 1922 onwards, treated battleships and battlecruisers identically, and the new generation of battlecruisers planned was scrapped under the terms of the treaty.