HMS Invincible, one of Britain's first battlecruisers

Battlecruisers (short for battleship-cruisers) were large warships of the early 20th century. They evolved from armored cruisers as new technology made it possible to build bigger ships. The main difference was their uniform main armament, compared to armored cruisers which had large and intermediate sized guns. Battlecruisers were of comparable size to a battleship and had the guns of a battleship but substantially thinner armor, the weight saving allowing more powerful engines to be fitted to give it greater speed.

The idea was that the big guns would allow a battlecruiser to take out destroyers and smaller cruisers before the battlecruiser ever got into range of their guns or torpedoes, while their speed would enable them to escape enemy battleships, or to swoop on crippled enemy battleships during a fleet action. The idea was mainly conceived by British admiral Jackie Fisher and summed up in his dictum, "speed is protection".

The first battlecruisers were the Royal Navy's Inflexible, Invincible and Indomitable, all completed in 1908. They had armour 6 or 7 inches (150 to 180 mm) thick along the side of the hull and over the gunhouses, whereas a comparable battleship of the period had armour 11 or 12 inches (280 to 300 mm) thick. Originally thought of as simply a new type of armored cruiser (their armour was the same as the preceding class of armored cruiser), they were then designated "dreadnought cruisers," and finally battle cruisers. These early ships had a top speed of 26 knots (48 km/h) compared to 20 to 21 knots (37 to 39 km/h) for contemporary battleships. They were armed with 11 in (German) or 12 in (British) (281 or 305 mm) guns, just like battleships. Soon after the British, the Germans started building their own battlecruisers, the first was Von der Tann of 1911. Von der Tann and most later German battlecruisers had only 11 in (280 mm) guns, but they were better armoured than British battlecruisers of the time.

In practice, battlecruisers rarely saw the type of independent action for which they were designed. In most cases, the temptation to add extra big guns to the main fleet proved hard to resist, and battlecruiser squadrons were added to the line of battle — a role for which they were not designed and which exposed them to great risk. It was found that their speed wasn't sufficient to protect them from the battleships' guns.

The original battlecruiser concept proved successful at the Battle of the Falkland Islands during World War I when the British battlecruisers Inflexible and Invincible did precisely the job they were intended for when they annihilated a German cruiser squadron commanded by Admiral Maximilian Graf Von Spee in the South Atlantic Ocean.

At the Battle of Jutland 18 months later, however, some of the British battlecruisers were employed as fleet units and engaged German battlecruisers and battleships before the arrival of the battleships of the British Grand Fleet. The result was a disaster for the Royal Navy: Invincible, Queen Mary and Indefatigable exploded with the loss of all but a handful of their crews, and Lion only survived by intentionally flooding one of her magazines. The German battlecruisers were better armoured, although Lützow was damaged and had to be scuttled, and Seydlitz was heavily damaged. No British or German battleship was sunk during the battle apart from the old German pre-dreadnought Pommern.

Thereafter, the Royal Navy de-emphasized battlecruisers. HMS Hood, launched in 1918, was the last British battlecruiser to be completed. Many nations chose to reduce their battlecruiser fleet following the Washington Naval Arms Limitation Treaty rather than scrap valuable battleships. Two battlecruiser hulls were converted into the Glorious-class aircraft carriers. Between the world wars, Hood was the biggest warship in the world. Her armour was stronger than that of earlier battlecruisers, but she exploded and sank in a duel with the German battleship Bismarck during World War II; the exact reason for her loss is still not known.

No other navies completed battlecruisers after this. The Imperial Japanese Navy converted its four battlecruisers of the Kongo class into "fast battleships", scrapped three of the four ships of the Amagi class under construction and converted the fourth, Akagi, into an aircraft carrier. The United States Navy retasked two battlecruiser hulls as aircraft carriers: USS Lexington and Saratoga were both designed as battlecruisers (the hull designations were originally CC-1 and CC-3) but converted part-way through construction, although this was only considered marginally preferable to scrapping the hulls outright (the remaining four: Constellation, Ranger, Constitution and United States were indeed scrapped).

USS Alaska, one of the United States Navy's few "large cruisers"

The US later built two battlecruiser-like "large cruisers" of the Alaska class, Alaska and Guam, which served effectively in World War II. These were large heavy cruisers, not battlecruisers proper: balanced designs armed with and armoured against 12 in guns, unlike traditional British-style battlecruisers which were not armoured against their own guns. Like the contemporary Iowa-class battleships, their speed made them ultimately more useful as carrier escorts and bombardment ships than as the sea combatants they were developed to be. A planned additional four ships of the Alaska class were cancelled after the war.

In the Naval Battle of Guadalcanal on 15 November 1942, a second battlecruiser–battleship engagement reinforced the inevitability of Hood's fate. One of Japan's Kongo-class "fast battleships", Kirishima, engaged the U.S. battleships South Dakota and Washington, and was destroyed by 75 hits from Washington; in contrast South Dakota survived 42 hits and was back in operation four months later.

The German Panzerschiffe (armored ship, also known as "pocket battleships") (Deutschland, Admiral Scheer, and Admiral Graf Spee), built to meet the 10,000 ton displacement limit of the Treaty of Versailles, were another attempt at a battlecruiser-like concept. Rather than construct a lightweight battleship which sacrificed protection in order to attain high speed, the pocket battleships were relatively small vessels with only six 11 inch (279 mm) guns — essentially large heavy cruisers. They attained fairly high speeds of 26 knots (52 km/h), and reasonable protection, while staying close to the displacement limit, by using welded rather than riveted construction, triple main armament turrets, and replacing the normal steam turbine power with a pair of massive 9 cylinder diesel engines driving each propeller shaft. The only action of significance they saw was the Battle of the River Plate, in which Admiral Graf Spee was cornered by a squadron of three cruisers.

The German ships Scharnhorst and Gneisenau were labelled battlecruisers, but they traded lighter armament, 11 in (279 mm) main guns, rather than thinner armor for speed, and could have been classified as light fast battleships. The French Dunkerque and Strasbourg were similar. These ships, like the Alaska-class, are not true battlecruisers. Battlecruisers are defined as distinct due to their mounting armament equivalent to that of the battleship and having insufficient protection against such armament.

Improved engine technology also worked against the battlecruiser formula. The ultimate limit on ship speed was drag from the water displaced (which increases as a cube of speed) rather than weight, so heavier armor slowed World War II battleships by only a couple of knots (4 km/h) over their more lightly armored brethren. As it turned out, however, aircraft carriers made both battleships and battlecruisers largely obsolete.

The Soviet Kirov class of Raketny Kreyser (Rocket Cruiser), displacing approximately 26,000 tons, is classified as a battlecruiser in the 1996-7 edition of Jane's Fighting Ships, even though in actuality they are very large missile cruisers. There were four members of the class completed, Kirov, Frunze , Kalinin , and Yuri Andropov . As the ships were named after Communist personalities, after the fall of the USSR they were given traditional names of the Imperial Russian Navy, respectively Admiral Ushakov, Admiral Lazarev, Admiral Nakhimov and Petr Velikiy.

See also

• List of cruisers

Further reading

• Bernard Ireland, Tony Gibbons, Jane's Battleships of the 20th Century (HarperCollins, New York, 1996) also covers battlecruisers