Under the command of Captain Louis Gabriel Deniéport, she sailed at the vanguard of the French Fleet on 20 October 1805, just before the Battle of Trafalgar, and she was the first Franco-Spanish ship to sight the English fleet, around 6 p.m. As the San Ildefonso surrendered to HMS Defence, Deniéport took advantage of a light wind to attempt to fill the gap in the line. She then found herself trapped between HMS Defiance and HMS Dreadnought, losing all of her rigging save for her lower masts.