Battleship

A battleship is a kind of large warship. It has metal armour and has large (heavy caliber) guns. Battleships are larger, better armed and armored than cruisers and destroyers. Battleships were mainly around from about 1880 to the 1940s, though some were still used as late as the Gulf War in 1991. For most of this time, battleships were the most powerful and most expensive kind of warship. Today some battleships are still around but these are museums.
In the 19th century, different countries tried to build bigger and better warships. One of the first ships with iron armor was called "Gloire", from 1859. This ship had both sails and a steam engine which drove a propellor, as well as guns the fired explosive shells. This was a kind of ship called an ironclad. A few years later, ironclads were used in the American Civil War.
Britain and France kept trying to build warships that were better than each other. Later in the 19th century other countries like Germany, Russia, Japan, Italy and the United States also built many battleships. Different countries used new inventions to make their ships more powerful, with things like steel armour, rifled guns, and better kinds of steam engine. By around 1890 people started to call their best ships 'battleships' instead of 'ironclads'. Many people, including many Admirals and politicians, thought battleships were very important. If there was a war, the country with the best battleships would win, by sinking the other side's navy and stopping them bringing food and goods into their country (called a blockade). But battleships were also very expensive, and other people thought it was better to spend the money on a better army, or things like pensions for old people. 
In 1906, Britain made a new kind of battleship called HMS Dreadnought. Though this ship was not much bigger, it had steam turbine engines which made it faster. All of its guns were also very large, which meant it could damage other battleships more from further away. People claimed one ship like Dreadnought could beat two earlier battleships, even battleships made just a few years before. Soon many countries were building ships like this, and calling them 'Dreadnoughts'.
Many battleships were used in the First World War. However, battleships were so important and expensive that neither side wanted to take a chance of losing a battle with them. There were several battles with battleships. The biggest one was the Battle of Jutland which involved dozens of battleships and hundreds of smaller ships. But none of the battles made much difference. Submarines made a bigger difference to the war, even though less people had expected them to. At the end of the War, Germany was made to hand over all their battleships to Britain. However, the German navy sank ("scuttled") their own battleships rather than give them to the British. In 1922, most countries which had big navies signed a treaty called the Washington Naval Treaty which meant no-one would build new battleships for at least 10 years.
Battleships were also important at the start of World War II. But by the middle of World War II, battleships had become less important than aircraft carriers. Aircraft carriers had dozens of airplanes which could drop bombs or torpedos. Even though battleships had thicker armour than ever, several hits from bombs or torpedos would still sink a battleship. The planes could fly much further than a battleship's guns could shoot. There were some important battles between battleships in World War II, but more often battleships were less important than aircraft carriers. At battles like the Battle of Taranto and the Battle of Pearl Harbour many battleships were sunk by planes.
After World War II there was not much point to a battleship. Aircraft carriers had become even better, because of jet aircraft and missiles. Also, even a heavily armored battleship could be sunk by a nuclear bomb. Even so the United States Navy kept a few battleships during the Cold War. The very big guns on a battleship were still useful to shoot at shore targets if there was an invasion from the sea. American battleships were also given new weapons like guided missiles to make them more useful if there was a war with Russia. However, only the United States could afford to keep battleships like this. No-one else did. Some American battleships shot at Iraq in the Gulf War. This was the last time when any battleships fought. The United States kept battleships until 2004, when the last ones were made into museums.