A fast battleship was a battleship which in concept emphasised speed without undue compromise of either armor or armament. Most of the early World War I-era dreadnought battleships were typically built with low design speeds, so the term "fast battleship" is applied to a design which is considerably faster. The extra speed of a fast battleship was normally required to allow the vessel to carry out additional roles besides taking part in the line of battle, such as escorting aircraft carriers.
HMS Queen Elizabeth, the first "fast battleship" of the Dreadnought era, in 1918
French battleship Dunkerque
USS Missouri, among the last "fast battleships", would serve until 1992
Figure 1. Concept that maneuverability and armament were more important than speed. A slower ship with larger guns could render a speedier ship's advantage moot.
The battlecruiser was a type of capital ship of the first half of the 20th century. These were similar in displacement, armament and cost to battleships, but differed in form and balance of attributes. Battlecruisers typically had thinner armour and a somewhat lighter main gun battery than contemporary battleships, installed on a longer hull with much higher engine power in order to attain greater speeds. The first battlecruisers were designed in the United Kingdom, 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.
HMS Hood, the largest battlecruiser ever built, in Australia on 17 March 1924
HMS Shannon, a Minotaur-class armoured cruiser
Invincible, Britain's first battlecruiser
HMS Queen Mary, the last battlecruiser built before World War I