The fort sits opposite the citadel of Château d'Oléron on the island of Oléron.

Fort Louvois consists of a horseshoe-shaped battery, with a tower redoubt or keep in the gorge or opening of the horseshoe.

The firing platform is 12 metres (39 ft) above the surface of the water, and the battery's lateral coverage is 180 degrees.

A barracks building on the fort's terre plein contained the arms room, food stores, and a water tank.

After the completion of the arsenal at Rochefort in 1666, Louis XIV wanted to create a chain of fortifications on the coast of Aunis and Saintonge.

A number of fortifications were built to defend the Rochefort, with Fort Louvois being the last commissioned under Louis XIV.

He wrote to Michel Bégon, the Naval Intendant at Rochefort, informing him that the king wished that a fort be erected on Chapus.

Because the islet was made up of shellfish and mud, the work was extremely difficult with the result that by 20 October only the stone foundations were in place despite the fact that the project had already expended more than half the funds budgeted for construction.

The German army took possession of the fort but withdrew within a day due to the Allied advance.

Free French forces then occupied the fort, only to come under fire from the Château d'Oléron, which was still in the hands of the German Army.