She underwent proving trials between September and November 1794 alongside the , also launched in 1794 but designed by Julián Martín de Retamosa (Romero de Landa's successor), aiming to work out whose method of construction was best. The trials were overseen by José Justo Salceno and the results favoured the
Montañés. The
Monarca was assigned to
Juan de Lángara's squadron, taking part in the defence of
Roses. She took part in the
battle of Trafalgar on 21 October 1805 under the command of Captain Teodoro Argumosa y Bourke. She was attacked at close range by and as they first cut the Franco-Spanish line. The ship behind the
Tonnant, , slipped under her stern at 12:30 and fired two broadsides into her. She was heavily damaged, with 100 men killed and 150 wounded. A party of 55
Royal Marines captured the ship, but the night after the battle the surviving Spanish crew overpowered them and cast them adrift, leaving them to the mercy of the storm that night. On 24 October the survivors decided to try to repair the ship's rudder and return to
Cádiz, as the weather was improving, but an hour later they were pursued by , which also picked up the marines and some Spanish survivors of the storm. On 28 October the ship ran aground on the Arenas Gordas coast near
Huelva, between
Torre de la Higuera and
Torre del Asperillo. On 31 October she was set on fire by the crew of the
frigate and blown up by order of
Vice-Admiral Cuthbert Collingwood. ==See also==