Fortified Sector of the Jura

The area was lightly fortified, since the Swiss border was regarded as a low-risk frontier, save for the possibility of an advance from Germany through Switzerland into France.

The Jura Mountains and the Doubs River presented natural barriers to invasion, allowing defenses to concentrate on a few points of potential access.

[3][4] At the midpoint of the Battle of France on 1 June 1940, the fortress troops of the SF Jura amounted to a chasseurs pyrénéens regiment in three battalions, comprising 85 officers and 2,750 men.

[5] The German offensive (Operation Kleiner Bär) across the Rhine was concentrated in the area near and to the north of Colmar, with little fighting in the Altkirch sector.

[6] Guderian approached the SF Jura from the rear, crossing the Doubs at Saint-Vit near Besançon.