Lost Battalion, in World War I, popular name given to those American units of the 77th Division—six companies of the 1st and 2d battalions of the 308th Infantry, one company of the 307th Infantry, and the platoons of the 306th Machine Gun Battalion—that were cut off by German forces after the launching of an American attack in the Argonne Forest in early Oct., 1918. The Lost Battalion, numbering about 600 men and under the command of Major Charles W. Whittlesey, put up a heroic five-day defense in the Binarville Ravine without food, water, or reserve ammunition. After withstanding several heavy barrages and attacks, the Lost Battalion, which defiantly refused the German demand of surrender, was rescued (Oct. 8, 1918) by American relief troops. Some 400 men of the Lost Battalion perished.

Tactical military organization composed of a headquarters and two or more companies, batteries, or similar units and usually commanded by a field-grade officer such as a lieutenant colonel. The term has been used in nearly every Western army for centuries and has had many meanings. In the 16th–17th century, it denoted a unit of infantry used in a line of battle and was loosely applied to any large body of men. During the Napoleonic Wars, battalions were fighting units of the French army under the administrative unit of the regiment. In the armies of the British Commonwealth nations, infantry battalions are tactical units within regiments. The typical U.S. Army battalion is a unit of 800–900 soldiers, divided into a headquarters company and three rifle companies; two to five battalions form the combat elements of a tactical brigade. Seealso military unit.

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