The Saint-Chamond (French pronunciation: [sɛ̃ ʃamɔ̃] ^ⓘ) was the second French tank to enter service during the First World War, with 400 manufactured from April 1917 to July 1918. It takes its name from the commune of Saint-Chamond where its manufacturers Compagnie des forges et aciéries de la marine et d'Homécourt (FAMH) were based.

Born of the commercial rivalry existing with the makers of the Schneider CA1 tank, the Saint-Chamond was an underpowered and fundamentally inadequate design. Its principal weakness was its Holt caterpillar tracks. They were much too short in relation to the vehicle's length and weight (23 tons). Later models attempted to rectify some of the tank's original flaws by installing wider and stronger track shoes, thicker frontal armour and the more effective 75mm Mle 1897 field gun.

Altogether 400 Saint-Chamond tanks were built, including 48 unarmed caisson tanks. The Saint-Chamond tanks remained engaged in various actions until October 1918, belatedly becoming more effective since combat had moved out of the trenches and onto open ground. Eventually, the Saint-Chamond tanks were scheduled to be entirely replaced by imported British heavy tanks.

In January 1915, the French arms manufacturer Schneider sent its chief designer, Eugène Brillié, to investigate tracked tractors from the American Holt Company, at that time participating in a test programme in England. The original French project was to provide mobility to mechanical wire-cutting machines of the Breton-Pretot type. On his return Brillié, who had earlier been involved in designing armoured cars for Spain, convinced the company management to initiate studies on the development of a Tracteur blindé et armé ("armoured and armed tractor"), based on the Baby Holt chassis, two of which were ordered.

Experiments on the Holt caterpillar tracks started in May 1915 at the Schneider plant with a 56 kW (75 hp) wheel-steered model and the 34 kW (45 hp) all-caterpillar Baby Holt, showing the superiority of the latter. On 16 June, new experiments followed in front of the President of the French Republic, and on 10 September for Commander Ferrus, an officer who had been involved in the study (and ultimate abandonment) of the Levavasseur tank project in 1908.

In early 1916, the first prototype of the Schneider tank was assembled in an army workshop. It featured tracks from the American-made Holt caterpillar tractors that were already used in France for towing heavy artillery. Private Pierre Lescure designed the fighting compartment. Lieutenant Fouché lengthened the tracks to improve trench-crossing ability. In this early form the prototype of the Schneider was called Tracteur A - not for security reasons, but because nobody knew exactly how to call such vehicles; the French word char was not yet applied to tanks. Eugène Brillié, the chief designer at Schneider, rejected this Tracteur A prototype. Instead he had invented a tail for his own tank's chassis thus providing the same trench crossing ability but for less overall weight and length.

While Brillié began to assemble this second prototype which was to become the Schneider CA1, the arms manufacturer Forges et Aciéries de la Marine et d'Homécourt (aka "FAMH"), based at Saint-Chamond, Loire, was given an order for 400 tanks by the French government, a political move prompted by General Mourret of the Army "Service Automobile". Saint-Chamond intended to build a tank that would be partly similar to the Schneider. Brillié refused to share his patents for free, and Saint-Chamond refused to pay. As a result, the "Forges et Acieries de la Marine et d'Homecourt" company, being unable to replicate certain patented details (notably the tail) of the new Schneider tank, developed its own proprietary design: the "Char Saint-Chamond". It included a "Crochat-Colardeau" gasoline-electric transmission, a traction system already used on railcars in service with the French railways. Furthermore, the freedom to design a heavier and larger tracked vehicle gave Saint-Chamond the opportunity to upstage the Schneider company. It did this by installing on its "Char Saint-Chamond" a more powerful, full size 75 mm field gun plus 4 Hotchkiss machine guns instead of the two machine guns present on the Schneider tank.

Saint-Chamond's technical director was Colonel Émile Rimailho, an artillery officer who had become dissatisfied over the insufficient reward he had received for helping design the famous Canon de 75 modele 1897 field gun as well as the Modele 1904 155 mm "Rimailho" howitzer. Following his departure from the French State arsenal system (APX) and joining Saint-Chamond, Rimailho adapted a Mondragon-designed 75 mm field gun for production for the Mexican Army. It was the proprietary Canon de 75mm TR Saint-Chamond (Modele 1915), designed to fire the regular French 75 mm ammunition. The French government had already made a commitment in May 1915 to purchase the Saint-Chamond 75mm gun. It is unclear whether the guns for the Saint-Chamond tanks were taken from existing stocks of Saint-Chamond guns or new production. Colonel Rimailho, who had a direct financial interest in selling his company's gun, induced the Ministry of War to specify that the new Saint-Chamond tank would also mount the Saint-Chamond made 75mm. In so doing Rimailho had also upstaged the Schneider CA1 tank which could only be fitted with a smaller Schneider-made fortress gun firing a 75 mm shell with reduced charge ammunition. To accommodate a regular length and full size 75 mm field gun, a hull longer than that of the Schneider tank was essential. The earliest Saint-Chamond prototype, a tracked vehicle longer and heavier than the Schneider tank was first demonstrated to the French military in April 1916.