The Obusier de 15 cm Tir Rapide Schneider-Canet-du-Bocage was a self-contained motorized howitzer system built by the French arms company Schneider-Creusot before the First World War for Portugal. The Schneider-Canet-du-Bocage howitzers are believed to be the first purpose-built motorized artillery system in the world.
Background
Although the majority of combatants had heavy field artillery before the outbreak of the First World War, none had adequate numbers of heavy guns in service, nor had they foreseen the growing importance of heavy artillery once the Western Front stagnated and trench warfare set in. Since aircraft of the period were not yet capable of carrying large-diameter bombs the burden of delivering heavy firepower fell on the artillery.
Large-caliber field guns often required extensive site preparation because the guns had to be broken down into multiple loads light enough to be towed by a horse team (max 8, ideally even 6) or the few traction engines of the time and then reassembled before use. Building a new gun could address the problem of disassembling, transporting, and reassembling a large gun, but it didn't necessarily address how to convert existing heavy weapons to make them more mobile. While rail transport proved to be the most efficient solution to moving large guns and their supplies road transport would be more flexible and able to operate in areas without fixed defenses or unsuitable for rail lines. Motorized road transport was a practical solution because the problems of heavy weight, lack of mobility, and reduced setup time were addressed.
History
In 1897 to increase their market share the Establishments Schneider du Creusot acquired the Ateliers d'Artillerie du Havre. As part of that purchase the engineer, Gustave Canet was added to Schneider et Compagnie's design team. Canet had by that time already designed many artillery systems and the guns from his Le Havre workshops were referred to as 'Schneider-Canet' guns for years after.
The concept for the Obusier de 15 cm TR Schneider-Canet-du-Bocage came from a Portuguese engineer Colonel Carlos Roma du Bocage who published a groundbreaking report called the Baterias moveis. Sua influencia na fortificaçao (The influence of mobile batteries on fortifications). In his report, du Bocage advocated a mobile defense strategy for Lisbon based on quick reaction forces with mobile self-contained howitzer batteries. At roughly the same time French Lieutenant Colonel Christophe Peigné began working on a proposal to mount artillery on rail carriages for use at the forts of Verdun, Toul, Épinal, and Belfort. Both Peigné and du Bocage were assisted by the Schneider engineer Gustave Canet. Unlike the du Bocage system the Peigné-Canet-Schneider mle 1897 gun carriage ran on narrow gauge rails installed at French forts.
By motorizing his howitzer batteries du Bocage was trying to solve several technical problems such as 1) Fixed fortifications are expensive to build, man, and maintain. An enemy isn't obligated to attack your fortifications and fortifications can't be built to protect everything. 2) If the guns of your forts face the wrong direction an enemy could attack from an unexpected direction where defenses were weaker. 3) Lacking mobility more guns would be needed to defend likely avenues of attack which would be wasteful because some guns would be engaged while others wouldn't. 4) Setup time for the guns would be reduced because the entire battery and their supplies would be transported assembled. 5) If the forts were overrun there wasn't a good way to evacuate the guns and they would be lost to the enemy. 6) Although rail transport was the most efficient form of transport available for both the guns and their supplies rail lines couldn't be laid everywhere to defend from an attack. Road transport could utilize existing road infrastructure and go where no fortifications or rail lines existed.