Warmatrix

Dreadnoughts were the largest battleships ever built. For several decades they dominated the seas, until cheaper but equally deadly weapons rendered them obsolete.
During the 19th century CE wooden sailing ships had given way to ironclads. In the last decade of that century armor was improved by a switch to steel and firepower by the adoption of quick-firing guns. This created 'pre-dreadnoughts', heavy battleships that outclassed the ironclads. A typical pre-dreadnought had a displacement of around 16,000 tons. Steam engines were able to push it to top speeds of around 30 - 35 kilometers per hour. Armor ranged in thickness from 5 - 10 centimeters on deck to 25 cm for the hull and 35 cm for the vital areas. It carried 4 heavy 30-cm guns; 6 - 18 smaller quick-firing guns ranging from 12 to 20 cm in caliber and numerous smaller guns. The heavy guns could penetrate the armor of enemy battleships; the lighter guns protected against cruisers, destroyers and torpedo boats. The longer range of the guns, together with improved range-finders, increased the distance at which battleships could effectively hit each each other from around 1.5 kilometers to 5 kilometers or more.
Another factor that prompted the urge to increase the range of the battleship guns was an increase in the range of torpedoes. Both pre-dreadnoughts and dreadnoughts proper carried torpedoes, though these proved to be very ineffective. However fired from submarines, they could be dangerous even to pre-dreadnoughts. Later true dreadnoughts proved tougher, though still vulnerable, so that most were escorted by a protective screen of destroyers.
Naval battles in the Russo-Japanese War showed that gunfire at long ranges could be effective and was necessary to come out on top. In response, several navies started to built heavier ships with larger guns. Britain was the first to complete one in 1906 CE: the HMS Dreadnought, which gave its name to a new class of battleships. The dreadnoughts dispensed with the variety of calibers and standardized all their main guns on the 30-centimeter caliber. This made the logistics of loading ammunition easier. The guns themselves also improved, so that heavy ones increased their rate of fire from 1 round per 4 minutes to 2 rounds per minute, as much as the earlier lighter quick-firing guns. Parallel improvements in gunnery made sure that all these also achieved a higher ratio of hits. The original Dreadnought displaced 18,000 tons and carried a crew of around 750 men. Steam engines were replaced by steam turbines, allowing it to reach speeds of 40 kilometers per hour, though they were not efficient at long distance cruising speeds. Countries that had access to oil used it to replace coal as fuel and equipped their ships with diesel engines. Armor ranged in thickness from 2 - 8 centimeters on deck to 28 cm for the hull and 31 cm for the vital areas. The Dreadnought carried 10 heavy 30-centimeter guns, plus an array of light guns.
Throughout the first half of the 20th century CE, bigger ships were designed and launched. Dreadnoughts gave rise to super-dreadnoughts, larger and armed with even more powerful guns. The heaviest battleships ever constructed were those of the Japanese Yamato class of 1937 CE. These displaced 70,000 tons, carried a crew of more than 2,700 men, had armor up to 65 centimeters thick and guns up to the 46 centimeter caliber. The heavy super-dreadnoughts were so expensive that navies could afford only a few of them; of the Yamato class only two were built. Other designs went in the opposite direction, sacrificing armor in exchange for speed. These were the 'fast' battleships and battlecruisers, capable of top speeds of around 50 - 60 kilometers per hour. They could keep up with lighter ships and outgun them, but had trouble dealing with heavy battleships.
The dreadnoughts were superior to the pre-dreadnoughts, rendering them obsolete. Their main disadvantage was high cost. The demand for firepower, armor and speed made it necessary to increase the size of the ships, to an average of 40,000 tons for full dreadnoughts. With it came a higher cost of materials, longer building time and larger crews. Nonetheless in the early 20th century CE navies around the world, especially Britain, Japan and the USA, engaged in an arms race to build as many dreadnoughts as they could. Several treaties tried to stop this competition, but none held long. The naval arms race was one of the factors that contributed to the outbreak of World War I.
In that war, dreadnoughts saw surprisingly little action, because their might deterred most enemies. Weaker and stronger fleets played cat and mouse with each other and most naval battles were fought by cruisers, destroyers and submarines instead, with the exception of the Battle of Jutland in 1916 CE. Despite that the arms race was resumed after the war. With further rising costs most countries could not keep up. Some built lighter, faster battlecruisers instead of battleships and some gave up alltogether. Pre-dreadnoughts, now fully obsolete, were scrapped and true dreadnoughts came to be called simply battleships.
In World War II battleships saw much more action than in the Great War, yet proved themselves half-obsolete. Lighter and cheaper weapons like destroyers, submarines and especially torpedo bombers wreaked such havoc among them that the queens of the sea faded away. They were reduced to a secondary role as coastal bombardment platforms. Their heavy guns gave good range and destructive power, but accuracy was poor. After the war almost all remaining battleships were converted or scrapped; some remained in use as coastal bombarders. The last ones were four American Iowa-class ships that were decommissioned in 1990 CE.