The French 75 mm field gun is a quick-firing field artillery piece adopted in March 1898. Its official French designation was: Canon de 75 mm Mle 1897. It was commonly known as the French 75, simply the 75 and Soixante-Quinze (French for "seventy-five"). The French 75 was designed as an anti-personnel weapon system for delivering large volumes of time-fused shrapnel shells on enemy troops advancing in the open. After 1915 and the onset of trench warfare, impact-detonated high-explosive shells prevailed. By 1918, the 75 became the main agents of delivery for toxic gas shells. The 75s also became widely used as truck mounted anti-aircraft artillery. They were the main armament of the Saint-Chamond tank in 1918 and the Char 2C.
The French 75 is widely regarded as the first modern artillery piece.Chris Bishop, "Canon de 75 modèle 1897", The encyclopedia of weapons of World War II, pg. 137Priscilla Mary Roberts, "French 75 gun", World War One, pg. 726 It was the first field gun to include a hydro-pneumatic recoil mechanism, which kept the gun's trail and wheels perfectly still during the firing sequence. Since it did not need to be re-aimed after each shot, the crew could reload and fire as soon as the barrel returned to its resting position. In typical use, the French 75 could deliver fifteen rounds per minute on its target, either shrapnel or melinite high-explosive, up to about away. Its firing rate could even reach close to 30 rounds per minute, albeit only for a very short time and with a highly experienced crew.
At the opening of World War I, in 1914, the French Army had about 4,000 of these field guns in service. By the end of the war, about 12,000 had been produced. It was also in service with the American Expeditionary Forces, which had been supplied with about 2,000 French 75 field guns. Several thousand were still in use in the French Army at the opening of World War II, updated with new wheels and tires to allow towing by trucks rather than by horses. The French 75 set the pattern for almost all early-20th century field pieces, with guns of mostly 75 mm forming the basis of many field artillery units into the early stages of World War II.
Development
The forerunner of the French 75 was an experimental 57 mm gun that was first assembled in September 1891 at the Bourges arsenal under the direction of Captain Sainte-Claire Deville. This 57 mm gun took advantage of a number of the most advanced artillery technologies available at the time: Vieille's smokeless powder, which was introduced in 1884. Self-contained ammunition, with the powder charge in a brass case which also held the shell. An early hydro-pneumatic short recoil mechanism that was designed by Major Louis Baquet. A rotating screw breech built under license from Thorsten Nordenfelt.
The only major design difference between the 57 and 75 that would emerge was the recoil system. But, in 1890, even before the 57 entered testing, General Mathieu, Director of Artillery at the Ministry of War, had been informed that Konrad Haussner, a German engineer working at the Ingolstadt arsenal, had patented an oil-and-compressed-air long-recoil system. They also learned that Krupp was considering introducing the system after testing it. Krupp would later reject Haussner's invention, due to unsolvable technical problems caused by hydraulic fluid leakage.
In 1891, Haussner sold his patents to a firm named Gruson, which searched for potential buyers. After reviewing the blueprints in February 1892, the French artillery engineers advised that a gun should be produced without purchasing the Haussner invention. Accordingly, General Mathieu turned to Lt. Colonel Joseph-Albert Deport, at the time the Director of the Atelier de Construction de Puteaux (APX), and asked him whether he could construct a gun on the general principle of the Haussner long-cylinder recoil without infringing the existing patents. After it was judged possible, a formal request was sent out on 13 July 1892.
It took five more years under the overall leadership of Mathieu's successor, General Deloye, to perfect and finally adopt in March 1898 an improved and final version of the Deport 75 mm long-recoil field gun. Various deceptions, some of them linked to the Dreyfus Case which erupted in 1894, had been implemented by Deloye and French counter-intelligence to distract German espionage.
The final experimental version of Deport's 75 mm field gun was tested during the summer of 1894 and judged very promising. Extensive trials, however, revealed that it was still prone to hydraulic fluid leakage from the long-recoil mechanism. The Deport 75 was returned to Puteaux arsenal for further improvements. Hydraulic fluid leakage was typical of this experimental phase of artillery development during the 1890s, as Haussner and Krupp had previously experienced.
In December 1894, Deport was passed over for promotion, and resigned to join "Chatillon-Commentry", a private armaments firm. Two young military engineers from Ecole Polytechnique, Captains Etienne Sainte-Claire Deville and Emile Rimailho, continued development and introduced an improved version in 1896. Their contribution was a leakproof hydro-pneumatic long-recoil mechanism which they named "Frein II" (Brake # II). A major improvement was the placement of improved silver-alloy rings on the freely moving piston which separated the compressed air and the hydraulic fluid inside the main hydro-pneumatic recoil cylinder. These and other modifications achieved the desired result: the long-term retention of hydraulic fluid and compressed air inside the recoil system, even under the worst field conditions.
Captain Sainte-Claire Deville also designed important additional features, such as a device for piercing the fuzes of shrapnel shells automatically during the firing sequence (an "automatic fuze-setter"), thus selecting the desired bursting distance. The independent sight had also been perfected for easy field use by the crews, and a nickel-steel shield was added to protect the gunners. The armored caissons were designed to be tilted in order to present the shells horizontally to the crews. The wheel brakes could be swung under each wheel ("abattage"), and, together with the trail spade, they immobilized the gun during firing.
The gun was officially adopted on 28 March 1898 under the name "Matériel de 75 mm Mle 1897". The public saw it for the first time during the Bastille Day parade of 14 July 1899.
Hydro-pneumatic recoil mechanism
The gun's barrel slid back on rollers, including a set at the muzzle, when the shot was fired. The barrel was attached near the breech to a piston rod extending into an oil-filled cylinder placed just underneath the gun. When the barrel recoiled, the piston was pulled back by the barrel's recoil and thus pushed the oil through a small orifice and into a second cylinder placed underneath. That second cylinder contained a freely floating piston which separated the surging oil from a confined volume of compressed air. During the barrel's recoil, the floating piston was forced forward by the oil, compressing the air even further. This action absorbed the recoil progressively as the internal air pressure rose and, at the end of recoil, generated a strong but decreasing back pressure that returned the gun forward to its original position. The smoothness of this system had no equal in 1897, and for at least another ten years. Each recoil cycle on the French 75, including the return forward, lasted about two seconds, permitting a maximum theoretical firing rate of about 30 rounds per minute.
The hydro-pneumatic system was treated as a state secret, and when the United States adopted the gun in 1917, the French military mission was reluctant to disclose the inner workings of the recoil system, leading one American officer to remark that "the French would sooner lose the war than lose the secret of the 75".
Ammunition At the beginning in 1914, the French 75 fired two main types of shells, both with high muzzle velocities (535 m/s for the shrapnel shell) and a maximum range of 8,500 metres. Their relatively flat trajectories extended all the way to the designated targets. French 75 shells, at least initially in 1914, were essentially anti-personnel. They had been designed for the specific purpose of inflicting maximum casualties on enemy troops stationing or advancing in the open.
A impact-detonated, thin-walled steel, high-explosive (HE) shell with a time-delay fuze. It was filled with picric acid, known in France as "Melinite", used since 1888. The delay lasted five hundredths of a second, designed to detonate the shell in the air and at a man's height after bouncing forward off the ground. These shells were particularly destructive to men's lungs when exploding in their proximity. A time-fused shrapnel shell containing 290 lead balls. The balls shot forward when the fuse's timer reached zero, ideally bursting high above the ground and enemy troops. During 1914 and 1915, the shrapnel shell was the dominant type of ammunition found in the French 75 batteries. However, by 1918, high-explosive shells had become virtually the sole type of 75 mm ammunition remaining in service.
Several new shells and fuses were introduced due to the demands of trench warfare. In 1918, a boat-tailed shell (with a superior ballistic coefficient) which could reach was deployed for use during the latter part of the war. Developed through French artillery research, it increased the effective range of the French 75 by about thirty-eight percent.
Every shell, whether it be a high-explosive or shrapnel shell, was fixed to a brass case which was ejected when the breech was manually opened. Semi-automatic breech opening and shell ejection during recoil and return had not been developed yet.
Rapid fire capability
The French 75 introduced a new concept in artillery technology: rapid firing without realigning the gun after each shot.Bidwell, Shelford, and Graham, Dominick, Fire-power — The British Army Weapons and Theory of War 1904–1945, Pen & Sword Books, 2004, pp 8–9 Older artillery had to be resighted after each shot in order to stay on target, and thus fired no more than two aimed shots per minute. The French 75 easily delivered fifteen aimed rounds per minute and could fire even faster for short periods of time, but the long-term sustained rate was 3-4 rounds per minute as more than this would overheat the barrel.Ian V. Hogg, 1971, The Guns 1914–18. . This rate of fire, the gun's accuracy, and the lethality of the ammunition against personnel, made the French 75 superior to all other regimental field artillery at the time. When made ready for action, the first shot buried the trail spade and the two wheel anchors into the ground, following which all other shots were fired from a stable platform. Bringing down the wheel anchors tied to the braking system was called "abattage". The gun could not be elevated beyond eighteen degrees, unless the trail spade had been deeply dug into the ground; however, the 75 mm field gun was not designed for plunging fire. The gun could be traversed laterally 3 degrees to the sides by sliding the trail on the wheel's axle. Progressive traversing together with small changes in elevation could be carried out while continuously firing, called "fauchage" or "sweeping fire". A four-gun battery firing shrapnel could deliver 17,000 ball projectiles over an area 100 metres wide by 400 metres long in a single minute, with devastating results. Because of the gun's traversing ability, the greater the distance to the enemy concentration, the wider the area that could be swept.
Service history World War I service