In 1804, Fulton switched allegiance and moved to Britain, where he was commissioned by Prime Minister William Pitt the Younger to build a range of weapons for use by the Royal Navy during Napoleon's invasion scares. Among his inventions were the world's first modern naval "torpedoes" (modern "mines"). These were tested, along with several other of his inventions, during the 1804 Raid on Boulogne, but met with limited success. Although Fulton continued to develop his inventions with the British until 1806, the crushing naval victory by Admiral Horatio Nelson at the 1805 Battle of Trafalgar greatly reduced the risk of French invasion. Fulton was increasingly sidelined as a result.