In 1874 a special commission under commander Mougin proposed an armoured casemate for a 138 mm gun. At that time the French industry was only able to produce flat metal plates. That is why the design of the casemate is quite simple. The embrasure can be closed with a turning disk. The casemate could only resist fire from field guns. That is why the four casemates were installed in the mountanous terrain between Epinal and Belfort where the use of siege guns wasn't expected. This casemate is the only one remaining.