Bavarian Crown Prince Rupprecht, commander of the German Sixth Army, was tasked with stopping the French invasion.

As the Germans moved in, what remained of the once-formidable First Army was hopelessly surrounded at Lille but counterattacked and resisted fiercely in a delaying action aiming to buy time for the beleaguered Anglo-French defenders of Dunkirk.

The French First Army liberated the southern area of the Vosges Mountains, including Belfort.

In February 1945, with the assistance of the U.S. XXI Corps, the First Army collapsed the Colmar Pocket and cleared the west bank of the Rhine River of Germans in the area south of Strasbourg.

In March 1945, the First Army fought through the Siegfried Line fortifications in the Bienwald Forest near Lauterbourg.

Operations by the First Army in April 1945 encircled and captured the German XVIII S.S. Armee Korps in the Black Forest and cleared southwestern Germany.

At the end of the war, the motto of the French First Army was Rhin et Danube, referring to the two great German rivers that it had reached and crossed during its combat operations.

These troops had played a major role in the liberation of Corsica (September–October 1943) and the Italian Campaign (1943–44), with about 130,000 men engaged.

[3] From September 1944 onward, 114,000 men of the French Forces of the Interior were added to the First Army, replacing many African troops.

In 1990 the army staff left Strasbourg and moved to the Château de Mercy in Mercy-lès-Metz, Moselle.