Mortier 280 mm TR de Schneider sur affût-chenilles St Chamond

The Mortier 280 mm TR de Schneider sur affût-chenilles St Chamond was a French self-propelled siege mortar designed during the First World War and used during the Second World War.

History
Before the First World War, the doctrine of the French Army was geared towards a war of rapid maneuver. Consequently, attention was focused on light mobile field guns such as the Canon de 75 modèle 1897 with little consideration given to heavy artillery. As the First World War settled into stalemate and Trench Warfare on the Western Front the light field guns that the combatants went to war with were beginning to show their limitations when facing an enemy who was now dug into prepared positions. Indirect fire, interdiction and counter-battery fire emphasized the importance of long-range heavy artillery.

The basic problem was how to deliver a large enough projectile to destroy deeply entrenched defensive positions. Since aircraft had not matured enough to reliably deliver large bombs on precise targets the burden fell on artillery. In order to address the French Army's lack of long-range heavy artillery, a number of surplus large caliber naval guns and coastal artillery pieces were converted to land use in order to provide fire support to armies in the field. In addition elderly siege artillery was brought out of retirement and a new generation of heavy artillery such as the Schneider 280 mm modèle 1914 mortar were built to overcome deeply entrenched defensive positions.

In order to deliver a large amount of explosives a large projectile needed to be fired from a large gun with correspondingly heavy weight. The size and weight of these artillery pieces became excessive and were beyond the ability of horse-teams to deliver in one piece. One answer was to make artillery pieces that could be broken down into smaller loads for transport by multiple horse-teams, but this meant large crews were needed to dismantle, transport and reassemble the pieces prior to use. Another answer was to mount large artillery pieces on railroad carriages so they could be quickly transported in one piece, but these were very heavy and could only go where tracks were laid. Both solutions were satisfactory as long as the front stayed stable but were inadequate for fluid warfare and unable to cross road-less stretches of no man's land.

As a result heavy artillery pieces were increasingly designed for motor traction by artillery tractors instead of horse-teams. An example would be the Holt tractor an early continuous track hauler used by Allies to tow heavy artillery. Another solution was to make the guns self-propelled and one of the first experiments was the British Gun Carrier Mark I but it was not a true self-propelled gun since the gun was dismounted to use.

Design
In order to address the problem of self-propelled artillery the French engineer Colonel Émile Rimailho working for the St Chamond company developed a complex solution consisting of two tracked vehicles. The first was an ammunition carrier which was powered by a gasoline engine which drove the ammunition carrier and drove an electric generator which provided power to the electrically driven gun carrier via an electric cable. While on-road the ammunition carrier could tow the gun carrier via a tow bar, while off-road the tow bar could be unhooked and the gun carrier could move independently while attached by an electric cable. Since the engine and generator were located on the ammunition carrier the gun carrier had a hollow center section so the gun could recoil below deck level and the gun could be mounted low on the chassis which improved stability. Since each track on the gun carrier had its own electric motor the two tracks could be moved independently so the vehicle could turn in place and this meant the gun did not need elaborate traversing gear.

Service
On March 2 1918 twenty-five were ordered from Saint Chamond and all were delivered during 1919 after the cessation of hostilities. Due to the end of the war, these were placed in reserve for future use. However, the Army wasn't satisfied with the system due to its slow speed and road damage caused by the weight of the system. Although mobilized as part of the general reserve during the Second World War they did not see much action due to their slow speed and many were disabled by their crews before capture. The Germans assigned captured examples the designation 28 cm Mörser 602(f) auf Selbstfahrlafette but limited numbers and poor serviceability prohibited their use.