Union was a Téméraire class 74-gunship of the line of the French Navy built at Lorient and launched in 1799. She was renamed Diomède in 1803. During the War of the Third Coalition, Diomède was part of a French force that sailed from Brest, France, on 13 December 1805 for what was planned as a 14-month cruise to attack British merchant shipping while avoiding combat with major Royal Navy forces. On 15 December 1805, the French force split into two squadrons which proceeded independently from one another. Diomède was part of the squadron under the overall command of Vice-AdmiralCorentin-Urbain Leissègues, which headed across the Atlantic Ocean bound for the Caribbean. During the voyage, Diomède suffered serious damage in a storm off the Azores in late December 1805. She arrived with most of the squadron at French-held Santo Domingo on Hispaniola on 20 January 1806, where Leissègues ordered the ships to be recaulked after their long and difficult transatlantic voyage. On the morning of6 February 1806, a Royal Navy squadron under the command of Vice-Admiral Sir John Thomas Duckworth arrived off Santo Domingo to attack Leissègues's force. Although several of Leissègues's ships were not yet ready for sea, Leissègues ordered them to get underway and sail westward along the coast of Hispaniola toward Nizao. In the resulting Battle of San Domingo, the French squadron maintained close formation, and the five French ships of the line formed a line of battle with Diomède third in line behind Alexandre and Impérial and ahead of Jupiter and Brave. Duckworth ordered his squadron to concentrate fire on the three leading French ships of the line, and accordingly the British 74-gun third-rate ship of the line opened fire on Impérial and Diomède simultaneously. As the engagement at the head of the French line became confused, with ships of the two sides intermingled and smoke restricting visibility, Diomède came across the 98-gun second-rate ship of the line and fired a heavy broadside into her, after which Atlas engaged her an close range. Spencer also resumed firing at Diomède. Impérial turned toward shore and Diomède followed her, and late in the morning both ships ran aground parallel to the beach on a reef off the coast of Hispaniola between Nizao and Point Catalan, suffering severe hull damage and losing all of their masts. As the British ships moved out of gunnery range, the crews of Diomède and Impérial assembled on deck to abandon ship. Diomède had suffered about 250 casualties. Leissègues ordered Diomède and Impérial burned as soon as their crews had completed their abandonment of the ships, but before that order could be carried out, boat crews from the fifth-ratefrigates and HMS Magicienne boarded them on 8 February 1806 and captured them without meeting any resistance. The British boarding party took 150 prisoners aboard Diomède including her commanding officer, CaptainJean-Baptiste Henry, and then burned her wreck.
