Argonne, Battle of the, major battle of World War I, fought in the autumn of 1918 between the United States First Army, which included the XVII French Corps, and strong units of the German army. Also called the Meuse-Argonne offensive, the battle was part of a general Allied offensive against the Hindenburg line, the highly fortified German defence positions in western Europe. The immediate objective of the First Army was to weaken these positions in the Argonne region of France; the secondary objective was to capture the chief German supply line, extending through Sedan and Mézières (both in France). On September 22, after a victory at Saint-Mihiel, France, the First Army, under the command of General John J. Pershing, began to move into the Argonne sector. By September 25, the line of the First Army extended from Regneville-Sur-Meuse, opposite Samogneux, in a south-westerly direction 32.2 km (20 mi) to La Harazée in the Argonne Forest above the valley of the Biesme River. This line was assigned to three army corps, the I, the III, and the V. Nine divisions formed the front line, and three were in reserve. French forces lay west of the Aisne River, and on the east the US position was flanked by French troops under US command. Opposed to the US forces were the German Fifth Army, with eight divisions, part of the German Third Army, and about eight divisions in reserve.

US operations were conducted in three stages, the first of which lasted from September 26 to October 1 and drove a salient about 11 km (7 mi) deep into enemy positions before the Hindenburg line. During the second stage, from October 4 to 16, the First Army crossed the Aire River and captured all major German defence positions in the Argonne region. The third, or pursuit, stage lasted from November 1 to 10.

In the Argonne offensive, more than 1,200,000 US troops were concentrated for the advance; of that number, 60,000 took an active part in the battle, which extended over an area of 1,295 sq km (500 sq mi). US casualties in the entire Battle of the Argonne were 117,000 killed or wounded. German losses were 94,000 killed or wounded, 26,000 captured by US forces, and 30,000 captured by the French. The battle caused the final breakdown of German resistance and helped bring about the German request for an armistice, which was granted on November 11, 1918.