The Gros Ouvrage of Mont des Welches was part of the Boulay sector and built on a relatively small scale. The fighting blocks are around 200 metres from the entrance and the ammunition train was hand hauled rather than supplied with overhead power. Mont des Welches had two artillery blocks plus machine gun and observation posts. It saw minor action in the Battle of France in 1940 and was later occupied by the Germans.
Post-war, it remained in the hands of the French Army until 1971. Small changes were made to the facilities during this period. After the army left, much of the fort was stripped - partly by local museums looking to improve the fixtures in preserved forts and partly by scrap merchants. Subterranea Britannica last visited in 2003 when there was also fire damage, probably through the burning of insulation off copper cables.
A few years later, around 2006, both entrance blocks were covered in earth and the fort is now completely sealed.