Fortified Sector of Thionville

The Fortified Sector of Thionville (Secteur fortifié de Thionville) was the French military organization that in 1940 controlled the section of the Maginot Line immediately to the north of Thionville. The sector describes an arc of about 25 kilometres (16 mi), about halfway between the French border with Luxembourg and Thionville. The Thionville sector was the strongest of the Maginot Line sectors. It was surrounded but not seriously attacked in 1940 by German forces in the Battle of France, whose main objective was the city of Metz. Despite the withdrawal of the mobile forces that supported the fixed fortifications, the sector successfully fended off German assaults before the Second Armistice at Compiègne. The majority of the positions and their garrisons finally surrendered on 27 June 1940, the remainder on 2 July. Following the war many positions were reactivated for use during the Cold War. Four locations are now preserved and open to the public.

The Thionville sector was part of the larger Fortified Region of Metz, a strongly defended area between the Ardennes to the west and the Sarre valley to the east. The Metz region was more important during the planning and construction phase of the Maginot Line than it was in the operational phase of the Line, when the sectors assumed prominence. The Fortified Region of Metz was dissolved as a military organization on 18 March 1940.

The sector was planned to protect Thionville, an important industrial city, and by extension, Metz, just to the south. Construction began in most places in 1930, and was largely complete by 1935. A reinforcing line was planned to back up the Cattenom salient, which protruded to the north between Bois-Karre and Galgenberg, with Kobenbusch forming the point of the northward projection. Two casemate groups and the petit ouvrage du Beysel were proposed but were never built. The reinforcing role was partially assumed by three ex-German fortifications, the Forts de Guentrange, Illange and Koenigsmacker, which encircled Thionville and possessed long-range artillery.

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