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 , 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 . Concept and organization . 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 . Command . The Thionville sector was under the overall command of the French 3rd Army , headquartered at Fort Jeanne d ' Arc at Metz , under the command of General Charles Condé , which was in turn part of Army Group 2 under General André - Gaston Prételat . The SF ( " secteur fortifiée " ) Thionville was commanded by General Cousse , then General Poisot from 1 January 1940 . The command post was in the Fort d ' Illange , south of Thionville . The interval troops , the army formations that were to provide the mobile defense for the sector , to support and be supported by the fixed defenses , were under the command of the Colonial Corps ( " Corps d ' Armee Colonial ( CAC ) " ) , General Fredenberg , commanding from the Château de Bétange . The Colonial Corps was in turn made up of the 2nd and 56th Infantry Divisions . Artillery support for the sector was provided by the 151st Position Artillery Regiment ( " Régiment d ' Artillerie de Position ( RAP ) " ) , which controlled both fixed and mobile artillery , commanded by Lt . Colonel Martin . The 2nd ID was made up of Class A reservists , while the 56th ID was a Class B reserve formation , not considered suitable for significant combat . Description . The sector includes , in order from west to east , the following major fortified positions , together with the most significant casemates and infantry shelters ( " abris " ) in each sub - sector : Sub - sector of Angevillers / Ouentrange . 169th Fortress Infantry Regiment ( " 169e Régiment d ' Infanterie de Forteresse ( RIF ) " ) , Chef de Bataillon Toussaint , command post at Bois de la Côte Peacetime barracks and support : Sub - sector of Hettange - Grande . 168th Fortress Infantry Regiment ( " 168e Régiment d ' Infanterie de Forteresse ( RIF ) " ) , Lt . Colonel Ferroni , command post at Sainte - Marie Pre - Maginot supporting fortification : Peacetime barracks and support : Sub - sector of Elzange . 167th Fortress Infantry Regiment ( " 167e Régiment d ' Infanterie de Forteresse ( RIF ) " ) , Lt . Colonel Planet , command post at the Fort de Koenigsmacker Peacetime barracks and support : History . Battle of France . During the early part of the Battle of France the SF Thionville was relatively quiet . Both sides kept up shelling and harassing attacks , but there were no major engagements in the sector in May and early June 1940 . Elsewhere , the situation was deteriorating fast . To the west , the German 16th Army was advancing up the valley of the Meuse to Verdun , aiming for Metz and Nancy . In the center , the German 1st Army had broken through at the Sarre on 15 June . To the east , the Rhine was crossed on the same day . German armies were moving freely behind French lines with the goal of encircling France ' s field armies , capturing the cities of Alsace and Lorraine , and cutting off the fixed fortifications . By mid - June , faced with the progressive collapse of the French First Army to the west , the interval troops began to pull back to avoid being encircled behind the Maginot Line . Measure A , issued by 3rd Army headquarters , called for the withdrawal of the interval troops on 15 June , protected by the casemates and " ouvrages " . Measure B was the withdrawal of artillery forces from the intervals late that day and into the 16th , protected by the " ouvrages " . Measure C was the withdrawal of all but skeleton forces from the fortifications . The forces left behind were to withdraw themselves by the 18th after sabotaging all equipment and weapons . Although the interval troops were able to temporarily escape , by the 17th the Thionville sector had been enveloped by the Germans from the east and west . Retreat was impossible for the fortress troops . On 21 June General Wilhelm Ritter von Leeb ordered all attacks against Maginot fortifications to stop , as a waste of resources . Action between the 21st and the date of the June 25 armistice was limited to sporadic shelling and , on the French side , to firing off ammunition at the Germans before it could be captured . Apart from determined German shelling of Block 5 at Rochonvillers , there were no significant attacks on Thionville sector " ouvrages " . Following the armistice , brief negotiations undertaken by the commandant of Kobenbusch settled on a formal surrender for the garrisons west of the Moselle on 30 June . No such negotiations took place to the east until French officers received confirmation directly from General Huntziger that they were to surrender their fortifications . The eastern positions of the SF Thionville were surrendered on 2 July 1940 Lorraine Campaign . While the main Maginot fortifications played no significant role in the Lorraine Campaign of 1944 , the pre - Maginot fortifications of Thionville posed a significant obstacle to the advance of American forces , most notably the Fort de Koenigsmacker . The U . S . 90th Infantry Division captured Koenigsmacker after three days of hard fighting on 12 November 1944 . " Môle de Rochonvillers " . Following World War II , the French military reclaimed the Maginot Line with the aim of renovating and improving it against a possible attack by Warsaw Pact forces . The strongest positions , Rochonvillers , Molvange , and Bréhain of the neighboring former SF Crusnes were designated the " môle de Rochonvillers " ( " breakwater " ) in 1951 and were placed back into service after a period of rehabilitation . " Petit ouvrage " Immerhof was included in this assemblage Lesser positions , such as Soetrich , Bois - Karre and Sentzich , were repaired and kept as government property , as were the remaining " gros ouvrages " in the sector , but were not formally designated as places of defense . After the establishment of the French nuclear strike force , the importance of the Line declined , and maintenance ceased in the 1970s , with most of the casemates and " petit ouvrages " sold to the public . Command centers . In the early 1960s , three " ouvrages " were renovated as military command centers . Rochonvillers was converted for use as a wartime command center for the Central Army Group ( CENTAG ) of NATO and was used for this purpose from 1961 to 1967 , when France withdrew from the NATO integrated command structure . In a similar manner , Molvange became the wartime command center for the 4th Allied Tactical Air Forces , again from 1961 to 1967 . The French military continued to make use of Molvange until 1999 . Soetrich saw a similar role in the 1960s . Rochonvillers was reactivated in 1980 as the wartime command center for the French First Army , operating in that role until 1998 . In each the comparatively spacious underground barracks , magazine space and utility areas were used and expanded . The combat blocks were not used and were sealed from the occupied areas . Present status . Immerhof , Bois - Karre and Galgenberg are operated as museums and are open to the public . The surface of Kobenbusch is a nature preserve with trails and interpretive signs . The lower levels of Kobenbusch have been flooded by the cooling water lake of the Cattenom Nuclear Power Plant , which was built on the site of the Camp de Cattenom . The Casemate du Grand Lot near Rochonvillers is occasionally open for tours . The Abri du Zeiterholz has been restored and is open for tours in the summer months . The Abri du Bois de Cattenom is occasionally open to visits . The remainder are either privately owned or are military property , abandoned and sealed . The pre - Maginot Fort de Guentrange is operated as a museum . The surface installations of the Fort d ' Illange are accessible to the public , and a similar public use is proposed for the Fort de Koenigsmacker .