It was assaulted by German forces during the Battle of France and was captured after a seven-hour bombardment.

The petit ouvrage[nb 1] was to be expanded in a second phase to gros ouvrage status with separate personnel and munitions entrances, two 75mm gun turret blocks and a 75mm gun casemate block.

The blocks are linked by an underground gallery system containing barracks spaces, ammunition storage and utility services.

[8] The Casernement d'Achen provided peacetime above-ground barracks and support services to Haut-Poirier and other positions in the area.

The Germans opened fire with 150 mm artillery at 1500 hours, concentrating on Block 3.