No single military power of World War 1 (1914-1918) invested in railway guns quite like the French. Such weapons proved of particular importance when the once-fluid war had bogged down into the slugfest known as "trench warfare". To dislodge the stubborn enemy from their footholds, existing, large-caliber guns - usually taken from coastal defense positions or expiring warships - were mated to specially-designed railway cars to produce the "railway gun". The weapons offered some relative mobility and armor protection and became the only means of bringing heavy artillery to bear on the enemy without the need for an army of men, support wagons, and pack animals.
Desperate for any and all heavy artillery, a French Army initiative born in October of 1914 called for the implementation of existing very-large-caliber (greater than 155mm) guns to serve in the role of land-based "mobile" artillery. The French scoured their inventory and found the suitable "Canon de 19C Modele 1870/93" available in some number. These guns were introduced back in 1893 and were originally developed for coastal fortifications to protect French shores and its interests. Internally, the guns were rifled for projectile stability through a hardened steel liner which was strengthened by iron "rings". Furthermore, these guns held the modern quality of being breech-loaded (de Bange design) as opposed to muzzle-loaded and could fire a 194mm projectile (separately-loaded bagged charge) supported by a hydro-gravity recoil mechanism every two minutes out to a range of 11.4 miles.
In 1915, twenty-six of the existing lot of 194mm L/30 guns were earmarked by authorities for conversion to railway guns. A large traversing turret (covered in steel plating) was devised to hold and turn these massive weapons about and all this was mounted atop an armored, four-axle railroad car manufactured by the Schneider concern. The end-result was a complete system weighing 65 tons, having a length of 48 feet, and fielding 19 foot long barrel assemblies showcasing hastily-arranged recoil systems for stabilization and a full-traversal mounting. The mounting component allowed for a full 360-degree turn as well as a -10 to +40 degree elevation span. The guns reached a rate-of-fire of two rounds-per-minute, fired their projectiles at an outgoing velocity of 2,100 feet-per-second, and - like their coastal gun counterparts - could range out beyond 11 miles.
Beyond the gun-carrying armored railway car section there was an accompanying artillery wagon that was equally armored (though, like the gun-carrying component, protection was only against small arms fire and shell splinters). These wagons were half the length of the gun section and sat atop a simpler twin-axle design.
As heavy and cumbersome as these systems were, and furthermore limited by the existing French railway network, they fit the bill during a time when aircraft and standard army artillery lacked the capability to deliver large war loads over range. Initial examples were made available to French fighting forces of France during April of 1915 and, despite their inherent limitations, were successful conversions and operated until the end of the war (1918). For their part, they became the first purpose-built, quantitative serially-manufactured railway guns of the war and showed the French dedication to this weapon type (Britain would follow later).
Amazingly, these systems remained in operable service into the World War 2 (1939-1945) period when big guns came into demand once more during the defense of France. However, with France beaten in May-June of 1940, the existing stock now fell to the conquering Germans and, ultimately, the Italians. The former reworked the guns for use as coastal defenses while the latter continued their use as armored train weapons with some local modifications enacted to suit battlefield requirements.