In the early years of the 20th Century, the French Army doctrine was to rely heavily on the Canon de 75 Mle 1897 to provide the mobility and fast rate of fire they considered necessary in modern warfare. However, they also invested in the Canon de 155 Mle 1904 CTR Rimailho to provide a heavier field gun with a high rate of fire. Unfortunately, as only 104 of these were available at the outbreak of WW1, the obsolete Canon de 155 L Mle 1877 had to be bought out of retirement in order to provide enough 155 mm howitzers to meet the Army’s needs.
By 1915, it was clear that in the type of trench warfare that had developed after the first year of war, the Mle 1877 could not provide the high rate of fire required and the Mle 1904 was too short ranged. The French Government therefore turned to both FAMH (often referred to as St Chamond from where they were based near Lyon) and Schneider and considered the heavy howitzers they had developed for export – St Chamond had developed a 150 mm howitzer for Mexico and Schneider had developed a 152 mm howitzer developed for the Russian Army. Modified versions of both of these were adopted as the Canon de 155 C Mle 1915 St Chamond and the Canon de 155 C Mle 1915 Schneider, respectively, where the ‘C’ stood for court or short in English.
The Canon de 155 C Mle 1915 Schneider was officially referred to as the C15S and used a similar carriage and recoil system as the earlier Canon de 105 L Mle 1913 Schneider (L13S). However, in order to reduce the cost of operating the C15S, it was modified in 1917 to fire bagged cartridges with the modified howitzer designated the Canon de 155 C Mle 1917 Schneider.
Carriage
The C15S carriage was similar in concept to that of the L13S. It consisted of a box trail with side arms in the front half that allowed space for the gun to recoil at higher elevation angles. A curved shield was mounted on the front of the trail to protect the gun crew with a hinged opening to allow for forward observation of the gun sights. The rear of the trail was provided with a spade to stabilise the gun during firing which was supplemented by brake shoes acting on the front of the wooden wheels operated via a rotary handle in front of the shield.
The gun pivoted on trunnions running in bearings at the top of the front of the trail with traverse provided by moving the trail sideways by up to 3 deg either side along the wheel axle. A traversing hand wheel was provided on both sides of the trail for this purpose that each rotated a screw thread inside a tube in front of the axle. This in turn moved a nut on the thread that was attached to the wheel axle resulting in the front of the trail being moved sideways along the axle.
The gun was elevated by means of a pair of large toothed arcs fitted either side under the gun cradle. An elevating hand wheel was provided on the left-hand side of the carriage which rotated a pair of elevating arc pinions via a gear train to provide fine adjustment of the gun’s elevation.
The gun was transported by either 8 horse or via motorised tractor. When horse drawn, the gun was hooked up to a two wheel limber as shown and, to balance the gun between the two sets of wheel, it was locked in the full recoil position.
Gun Design
The C15S gun was 2.332 m or 15 calibres long and was of built-up construction as was normal during the early part of the 20th century. The gun consisted of a rifled tube with a chamber for the projectile and brass cartridge at the rear behind which was an interrupted threaded section for the breech. A jacket was shrunk over the rear portion of the tube with fittings to the breech mechanism.
An interrupted screw breech was used with a single motion lever that, when operated, rotated the breech screw to unlock it before swinging it clear of the breech opening. At the same time an extractor ejected any spent cartridge. The centre of the breech was fitted with a striker that was struck by a large spring loaded hammer (marteau) to set off the shell cartridge. The hammer was cocked manually and released via a lanyard.
Recoil System
Unlike the German and British field howitzers used in WW1 which used hydro-spring recoil systems, the C15S used a much more sophisticated hydro-pneumatic recoil system. The C15S recoil system was contained within the cradle (berceau) on a recoil sled (traineau) which recoiled with the gun attached along runners either side of the cradle. The cradle extended some distance behind the breech to allow the gun to be fully supported for the full length of recoil.
Within the recoil sled, there were two cylinders in the lower part with the right-hand one forming the hydraulic buffer (frein) and the left-hand one forming the recuperator (recuperateur). At the front above these cylinders were 2 reservoirs for the recuperator. The hydraulic buffer is shown at the bottom of the cutaway drawing below which was drawn for clarity with the buffer and the recuperator one above the other rather than side by side.
The hydraulic cylinder was filled with oil and contained a piston on the end of a tube attached to the front of the cradle so that, as the gun recoiled, the cylinder moved backwards while the piston stayed still. The piston contained small ports to restrict the flow of oil past it during recoil and, in so doing, absorbed most of the recoil energy helped a little by the air pressure in the recuperator. The hollow piston tube (tige de frein) was also filled with oil and contained another piston on the end of a rod (contretigre) attached to the rear of the recoil sled. The purpose of this inner hydraulic buffer was to absorb the energy generated by the recuperator in order to bring the gun to a gentle stop when it was returned to battery.
The recuperator is shown just below the large reservoir in the cutaway drawing above and was responsible for returning the gun to battery after the recoil ended. The recuperator consisted of a cylinder in the lower part of the recoil sled, which recoiled with the gun, and a piston on the end of a rod fixed to the front of the cradle. As the cylinder moved backwards, the oil in front of the piston was forced into the two large (grand) reservoirs at the front of the recoil sled thus compressing the air inside. Once the recoil had stopped, this increased air pressure then forced the gun forward back into battery. The ambient air pressure was maintained at 500 psi.
Unlike the equivalent British Ordnance QF 4.5-Inch Howitzer, the C15S did not have to use a cut-off gear to restrict the length of recoil as the gun was elevated as there was always sufficient clearance for the recoiling breech above the ground. The maximum recoil distance of the gun was 1.30 m.
Sighting
The sights were mounted on a bracket fixed to the end of the left-hand gun trunnion and therefore elevation with the gun. As with nearly all howitzers, the sights were reciprocating to allow them to compensate for the carriage wheels not being level, which was the norm. Ignoring spin drift, the shell trajectory normally lies in the vertical plane through the gun barrel. However, if the wheels and therefore the gun trunnions are not horizontal, this trajectory plane will be rotated away from the centre line of the gun cradle in the direction of the lowest wheel resulting in a large sighting error. To eliminate this effect, the sights were mounted on a reciprocating bracket that could be tilted sideways about an axis parallel to the gun to put the sights back into the same vertical plane as the projectiles. This tilting was performed using the knurled knob (bouton molete) and the cross-level bubble (niveau d’inclinaison) at the rear of the sight.
The required tangent elevation was set on the sight using the large knurled knob at the rear of the sight assembly which controlled the height of a toothed arc on which the sights were mounted- when raised, this tipped the sights forward with a tangent elevation scale provided marked in milliemes (the same as a NATO MIL with 6400 to 360 degrees). A clinometer was provided above the elevation adjustment knob consisting of a level bubble (niveau de tir) and a pair of knobs to set the angle of sight from -500 to -500 milliemes . To set the gun to the required quadrant elevation to hit a target at a particular range, the angle of sight and the tangent elevation was set on the sight and then the gun was elevated until the clinometer bubble was level.
The C15S was mainly used for indirect fire where the target was not visible in the sights. However, the sights used were developed before the adoption of an effective panoramic sighting telescope (goniomètre panoramique) became available and instead used a goniometer (goniomètre) mounting a collimator on top of a rotatable column as the main sighting device. The goniometer was fixed in a socket at the top elevating arc. The collimator sight itself consisted of a rectangular hood through which the target was viewed together with a small collimator in the lower part. The collimator generated a cross-hair reticule in the field of view of the sight effectively focused at infinity. Therefore, when looking through the sight hood, the gun layer saw the target with the reticule superimposed on it with very little parallax. In use, the gun layer positioned his head about 10 inches behind the sight to use it properly.
The mortar was layed for direction using a suitable fixed aiming point that could be viewed in the sight. The offset bearing from the aiming point to the target was set on the collimator sight using the crank handle (manivelle du plateau mobile) and the fine and coarse bearing scales. The inclination of the field of view of the collimator sight could be changed using the tilt knob (molette de l’arbre d’inclinquetage). The aiming point for the sight could be chosen to be in front of the gun, to the side of it or to the rear. To enable an aiming point to be used behind the gun, the collimator sight was provided with a prism (prisme de reperage en arriere) providing a rear view past the sight.
Ammunition
The C15S used brass cartridges with 6 different charges (00, 0, 1,…5) and muzzle velocities available. The following projectiles were used with the C15S where the bottom two projectiles are Shrapnel shells and the rest are high explosive.
Canon de 155 C Mle 1915 Specifications
- Length: 7.78 m
- Maximum Width: 1.52 m
- Wheels: Wooden 1.33 m in diameter
- Weight of Gun & Carriage: 3220 kg
- Length of Gun: 2.332 m or 15 calibres
- Bore: 15.5 cm
- Muzzle Velocity: 450 m/s
- Maximum Range: 11,200 m
- Trail: Box trail
- Recoil System: Hydro-pneumatic
- Maximum Recoil: 1.30 m
- Rifling: Uniform 1 turn in 25 calibres
- Length of Rifling: 1.764 mm or 11.4 calibres
- Twist: Right-hand
- Grooves: 43
- Firing Method: Percussion
- Elevation: 0° to +42°
- Traverse: -3° left to +3° right
