Departing Departing from Brest on 13 December 1805 , it was 12 days before the Admiralty in London were aware of the French movements , by which time the French squadrons were deep in the Atlantic , one under Vice-Admiral Corentin-Urbain Leissègues intending to cruise Self_motion in the Caribbean and the other , under Contre-Admiral Jean-Baptiste Willaumez , sailing Self_motion for the South Atlantic .