How a Chauchat works

The Chauchat was the standard light machine gun or "machine rifle" of the French Army during World War I (1914–18). Its official designation was "Fusil Mitrailleur Modele 1915 CSRG" ("Machine Rifle Model 1915 CSRG"). Beginning in June 1916, it was placed into regular service with French infantry, where the troops called it the FM Chauchat, after Colonel Louis Chauchat, the main contributor to its design. The Chauchat in 8mm Lebel was also extensively used in 1917–18 by the American Expeditionary Forces (A.E.F), where it was officially designated as the "Automatic Rifle, Model 1915 (Chauchat)". A total of 262,000 Chauchats were manufactured between December 1915 and November 1918, including 244,000 chambered for the 8mm Lebel service cartridge, making it the most widely manufactured automatic weapon of World War I. The armies of eight other nations – Belgium, Finland, Greece, Italy, Poland, Romania, Russia, and Serbia – also used the Chauchat machine rifle in fairly large numbers during and after World War I.

The Chauchat was one of the first light, automatic rifle-caliber weapons designed to be carried and fired by a single operator and an assistant, without a heavy tripod or a team of gunners. It set a precedent for several subsequent 20th-century firearm projects, being a portable, yet full-power automatic weapon built inexpensively and in very large numbers. The Chauchat combined a pistol grip, an in-line stock, a detachable magazine, and a selective fire capability in a compact package of manageable weight (20 pounds) for a single soldier. Furthermore, it could be routinely fired from the hip and while walking (marching fire).

The muddy trenches of northern France exposed a number of weaknesses in the Chauchat's design. Construction had been simplified to facilitate mass production, resulting in low quality of many metal parts. The magazines in particular were the cause of about 75% of the stoppages or cessations of fire; they were made of thin metal and open on one side, allowing for the entry of mud and dust. The weapon also ceased to function when overheated, the barrel sleeve remaining in the retracted position until the gun had cooled off. Consequently, in September 1918, barely two months before the Armistice of November 11, the A.E.F. in France had already initiated the process of replacing the Chauchat with the M1918 Browning Automatic Rifle. Shortly after World War I, the French army replaced the Chauchat with the new gas-operated Mle 1924 light machine gun. It was mass manufactured during World War I by two reconverted civilian plants: "Gladiator" and "Sidarme". Besides the 8mm Lebel version, the Chauchat machine rifle was also manufactured in U.S. .30-06 Springfield and in 7.65×53mm Argentine Mauser caliber to arm the American Expeditionary Forces (A.E.F.) and the Belgian Army, respectively. The Belgian military did not experience difficulties with their Chauchats in 7.65mm Mauser and kept them in service into the early 1930s. Conversely, the Chauchat version in U.S. .30-06 made by "Gladiator" for the A.E.F., the Model 1918, proved to be fundamentally defective and had to be withdrawn from service.

The Chauchat is the only full-automatic weapon actuated by long recoil, a Browning-designed system already applied in 1906 to the Remington Model 8 semi-automatic rifle: extraction and ejection of the empties takes place when the barrel returns forward, while the bolt is retained in the rear position. The failure of its limited version in U.S. 30-06 (the Mle 1918) have led some modern experts to assess it as the "worst machine gun" ever fielded in the history of warfare. However the weapon did remain in active service for over two years during the First World War, was the most widely issued fully automatic light machine gun of that conflict and remained in service after the war ended with several armies.