Fortified Sector of Mulhouse

The Fortified Sector of Mulhouse (Secteur Fortifié de Mulhouse) was the French military organization that in 1940 controlled the section of the French frontier with Germany in the vicinity of Mulhouse. The sector's principal defense was the Rhine itself, which could be crossed only by boat or by seizing a bridge crossing. The sector's fortifications chiefly took the form of casemates and blockhouses. The sector did not see significant action during the Battle of France, since the German crossings of the Rhine took place further north, near Colmar. The fortifications in the sector were built as part of the overall plan for the Maginot Line, but did not include the major fortified positions that characterized the Maginot Line of northeastern France. The sector did not see significant fighting in World War II. It was bordered to the north by the Fortified Sector of Colmar and on the south by the Fortified Sector of Altkirch.

The fortifications of the Mulhouse sector were laid out in two major lines, one right on the Rhine, and another to the rear on the eastern edge of the Hardt forest. No fortifications were established south of Hombourg, owing to the provisions of the 1815 Congress of Vienna treaty, which forbade permanent fortifications within 12 kilometres (7.5 mi) of Basel. Two positions were placed between the front and rear lines, and were considered a second line. The fortifications consisted entirely of casemates and blockhouses, constructed by the Commission d'Organisation des Régions Fortifiées (CORF), CORF was responsible for the major fortifications of the Maginot Line, but in this area no major positions or ouvrages were built. The Hardt forest was regarded as a significant obstacle between the third line and Mulhouse.

The riverbank fortifications were of a basic nature, with protection only up to 155mm caliber, machine gun armament and no electrical system. The second and third lines were more robust in construction and equipment, with electric generators and anti-tank weapons. The heaviest concentration of fortifications were in the area of Neuf-Brisach, itself a preserved fortress from the Vauban era. Neuf-Brisach guarded a strategic bridge across the Rhine.

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