A dreadnought is a navy battleship. A battleship is a large ship used in ocean battles between countries. The first dreadnoughts were made in the early 20th century. They were named after HMS Dreadnought, of the Royal Navy, the first ship of that type.
The first dreadnought was launched in 1906 by the United Kingdom, and was a new design of battleship. These ships had bigger guns; they also had guns that could shoot longer distances. Heavy steel layers were built on to the dreadnoughts as protection, which made them very strong and hard to sink. They were also much faster than older battleships. World War 1 was the first war in which dreadnoughts were used. After the war, a treaty was signed in Washington DC to limit the construction of battleships. This treaty helped stop the manufacturing of dreadnoughts. Japan, the UK, France, Italy and the United States signed this treaty.