The Fusil Mitrailleur Modéle 1915, more commonly known as the Chauchat (pronounced "Sho-sho"), is a French light machine gun.
The Chauchat was adopted in 1912 when the French did not have any sort of weapon for suppressive fire engagements. It was used in trench warfare, but without much success due to these trenches exposing a few flaws with the Chauchat. It was used until 1945, where it was completely replaced by the FM 24/29.
An aircraft variant known as the Chauchat Sutter CS 1913 also existed. It had an overhead magazine and an alloy pistol grip section and stock.
The Chauchat used a long-recoil system, similar to the Remington Model 8 and the M1941 Johnson, where the barrel would move back a short distance every time the gun fired. The Chauchats had a very odd-looking magazine that held 20 rounds; this was one of the main sources of problems for said weapon. The Chauchat magazines had openings on each side, allowing the gunner or loader to see how much ammunition was left. However, this came at a cost. When the Chauchats were used in trench warfare, dirt usually got into the openings on the side of the magazine, jamming up the gun and rendering it useless.
The Chauchat is notorious for being one of the worst firearms ever designed. Oddly enough, the 8mm Lebel version, even with its oddly-shaped magazine, was actually a rather reliable gun. However, the .30-06 version of the Chauchat was truly one of the worst guns ever made, likely due to a poor conversion from 8mm Lebel to .30-06. It is unclear as to why the Chauchat could not be successfully converted to .30-06 Springfield despite successful conversions to 7.92x57mm Mauser. As a lot of deactivated Chauchats exist, in order to preserve the Chauchat's notoriety, the deactivated Chauchats were poorly reactivated so that they would have some faults.