The duc d'Harcourt, governor of Normandy, and Suffren, Lieutenant général des armées navales, had been ordered by Louis XVI to build a major military port on France's north-west coast.

In 1776 they thus put La Bretonnière and Pierre Méchain in charge of perfecting the mapping of the coast between Dunkirk and Granville.

However, work initially proceeded according to the more innovative plan of Louis-Alexandre de Cessart to sink 90 wooden tree trunks into 20 m high piles and cladding them with stone.

In 1784 Cessart was made chief engineer of the project and La Bretonnière returned from America as Cherbourg's naval commander.

Bonaparte, then first consul, let La Bretonnière back into the navy at the rank of captain in 1803 but refused to let him return to the building project at Cherbourg, instead putting him in command at Boulogne then Dunkirk.