The famous French "75" in detail

The French "75" - or to be more precise: Canon de 75, modèle 1897 - was a new and revolutionary piece of weaponery, as revolutionary as other remarkable inventions that changed the face of battle, say, the bayonet or the breech loading rifle. Up til this point the carriages of all guns had been rigid and fixed, meaning that when the piece was fired, the whole gun rolled backwards due to the recoil. And this had been the standard procedure since the Middle Ages. There were of course several problems with this. The biggest one, was that it lowered the rate of fire: firstly because the gun had to be relaid between each shot, as it rolled out of position for each discharge, secondly because that the whole rolling backwards and forward delayed the whole reloading process. All this was changed with the "75".

        

The truly great invention, and a tribute to French engineering skills, was of course the hydro-pneumatic recoil system, that allowed the whole recoil to be absorbed by the carriage. The gun tube rests on a cradle, and when fired, the tube moves backward, pushing a floating piston back in another part of the cradle, the so called recuperator, which is filled with air. The air is compressed by the force of the piston, soon spent as the recoil reaches it's maximum, and then the compressed air forces the piston the other way, pushing the barrel back forward into the cradle. This is, in simplified terms , the workings of a hydro-pneumatic recoil system.

        

But this wasn't the only invention in the "75". The "75" was really a whole system of new concepts. The hydro-pneumatic recoil system was also combined with A) a so called trail or earth spade, at the end of the trail, that cut into the ground, holding the gun steady - of course an impossibility in a rigid carriage, as this would have caused the gun to topple over du to the force of the recoil, and B) what the french called an Abatage, or wheel anchor: the abatage fixed the wheels as well with the help of a metal shoe, placed underneath the wheels, rigidly attached to the trail, when the gun was sited. 

This meant that the gun - if properly placed - could be fired without moving at all, which meant A.) that the gun layer didn't have to relay the gun after each shot, perhaps only checking it, and B.) that it could be reloaded a whole lot faster, as the loader only had to wait for the gun tube to recoil back, before putting another round into the breech. (Also: the gun layer only had the responsibility for the side sighting: the elevation was left to the breech operator to the right, an arrangemant that also speeded up the working of the gun.)

To see some actual WW1 footage of a "75" being fired, click here!

But this wasn't all. The breech was also of a special screw type that could be operated very fast, and that also incorporated a special security latch that prevented any accidental opening of the breech, say, in case of a mis-fire. To this must also be added two ther components: A.) fixed ammunition, where the shell and the cartridge case - with the propellant - were permanently attached, with no need for several stages of loading, and B.) - and this was also really novel - an automated fuse setter. 

The French used Time Fuses on all their shells, HE or shrapnel, and the usual procedure is to set them up by hand, using a special wrench. In this vase the French constructed an automatic fuse setter, that looked like a box, with a dial for setting the fuse times, two handles, and two holes; into these holes the shells were dropped, fuse first, and then the handles were turned, causing an automatic setting of the fuse, to the numbers given on the dial. Simple, elegant - and fast.  

  

At the outbreak of the war in 1914, the "75" was the main gun of the French Field Artillery. Every Division had one Artillery Regiment attached, consisting of three groupes, each with three batteries equipped with four guns, or 12 guns per groupe, or 36 guns per Artillery Regiment. The Army had a total of 1.011 of these 4-gun-batteries in service in August 1914. 

You could very well say that the "75" was the main gun of the French Army in 1914, period. The French had an enormous faith in this fenomenal gun, with it's tremendous rate of fire, ease of maneuver (it was light) and accuracy. The gun was also very sturdy. The problem was, that the gun was intended for a classic war of maneuver, and as soon as the trenches were dug stalemate started, the deficiencies of the gun, and well, of the whole concept, became clear.

       

It was essentialy a Direct Fire gun, which explains why it had such a high muzzle velocity (higher than, say, it's german counterpart, the FK 96 n.A.) which, in turn, gave the shells a very straight and level trajectory. This is, of course, fine in Direct Fire, but if you are to reach targets behind obstacles or masked by terrain, this becomes a problem, especially if the targets are at that close range, when the shell trajectory is virtually level. Then you can't hit hem! 

For this you really need to supplement the "75" with a plunging trajectory, i.e. a howitzer, something that French didn't have - unlike both the Germans and British, which both fielded Light Howitzers to use in situations like these. The French introduced a stop-gap measure, the so called Malandrin Discs, that were clipped to the shell to spoil its aerodynamic qualities, and force it to drop sooner. These discs - there were two variants - were not really successful: for one thing, they badly reduced the accuracy of the shell.

       

Another problem was the munitions of the "75". Firstly, the main ammunition of the gun, Shrapnel and High Explosive Shell, were really not effective against dug-in targets. The Shrapnel shell packed 290 lead bullets, and weighed 7.2 kilos. The HE shell weighed only 5.5 kilos, and the explosive charge consisted of 800 grams of Melenite. While devastating against troops in the open, the Shrapnel was virtually useless against an entrenched opponent. 

The HE shell was a bit too light, packing too small a punch to penetrate entrenchments. In trench fighting, the "75" - as were the Field Guns of the other nations - was often given the role of supplying suppressing fire, especially at night, leaving the really effective firing to trench mortars and howitzers. And because the He shell was so light, it had a much shorter maximum range (5.500 meters) than the Shrapnel Shell (8.500 meters). 

The range was however increased, partly by new rounds, with cartridges with an increased amount of propellant and shells with more aerodynamic shape, heavier wight and bigger explosive charge, partly by increasing the elevation by digging a hole for the trail.

       

Another problem with the munitions concerned the fuses. At maximum range, or in difficult terrain there were an unacceptable proportion of duds or blindgänger, as the Germans called them (literally "blind walkers"). 

Also the fuses were a bit tricky, and especially in the beginning of the war there were many instances were the shells detonated in the gun tube, destroying the gun, killing and or wounding the crew. In fact, in January 1916 this was by far the most common cause for "75":s being lost. Up to that date 1.600 "75":s had been destroyed or damaged due to faulty munitions. At the same time, only 400 had been lost as a result of enemy action! This problem was never really solved, as improvements in the fuse mechanics were often nullified by the lowered quality of workmanship that came as a result of the stepped up mass-production of munitions.

           

Anyway, dispite these problems, it remained a formidable gun, that, if the conditions were right, could make a very telling effect indeed. And it is a testimony to the excellence of this gun, that it was also adapted by the US Army, and later also by the armies in Poland, Greece, Portugal, Romania, Portugal, Estonia and Lithuania. It was also used in WW2, not only by the French, but also by the Finns, and the Germans.

The excellently preserved gun and caisson below can be seen in the War Museum in Fleury, right on the famous Battlefield outside Verdun:

The "75" below is to be found in a museum in USA, and is photographed by Mike Casale, NJ. The gun was the first to be used by US Forces in WW1, and has been preserved since. It is a VERY interesting suite of pictures, as it shows an almost mint example of authentic WW1 French-style camouflage. Note the colours!

       

It is said that a lot of guns were destroyed by misfiring ammunitions. This is true, and the figure given are correct, but, this phenomenon didn't occured mostly, as you write, in the beginning of the war. Actually, shells fired for the first weeks of the war, until the end of the "race to the sea" operations, belonged to pre-war stock, which were of sound quality, material and manufacturing wise. Most chamber explosions occured from Spring 1915, during 1st Champagne and Artois offensives, where the 75mm munition consumption overtook the 1914 rates by far, to 1916 (Somme and Verdun), where both offensive and defensive large operations needed huge numbers of shells. By late 1916, however, gun explosions became less frequent and finally nearly disapeared in the following years.

   

Several explanations had been proposed.

This phenomenon, an abnormal chamber and tube wear, increased by this gun high rate-of-fire, was indeed due to faulty munitions, but particularly including those manufactured in the USA (French government had urgently ordered huge numbers of them by late 1914), not only because of poor workmanship in mass production (be it French or US), but because mechanical fitting trouble between metric (guns) and imperial system (US made munitions). (Although it can sound weird, the same kind of mechanical fitting problem occured with narrow guauge RR engines manufactured by Baldwin on French blueprints. Fortunately, the results, in this case, were far less dramatic.) The fact is that huge numbers of US-made 75mm ammunition were banned from use, at least in operational conditions.

   

Concerning workmanship: given the size of pre-1914 US war industry, there is no doubt that the US manufacturers the French governement used had probably no more experienced workers than the French industry itself, but the most experienced French workers were on the frontline.

Eventually, although mass production of 75mm munitions kept on until the end of war, as this weapon remained the "backbone" of French artillery, the phenomenon of chamber or tube explosions decreased to marginal levels.

For more info (in French) on the "75", click here!

 

Calibre	75mm
Weight of gun (emplaced)	1.160 kilos
Maximum Range	5.5 km (HE) 8.5 km (Shrapnel)
Muzzle Velocity	584 metres/second
Min/Max Elevation	-12/+18
Weight of Shell	5.5 kilos (HE) 7.2 kilos (Shrapnel)

Many companies produce kits of this gun, most of them for the Wargaming market, and many of these are simply too simplified. Very good kits are made by AL.BY (but of course!), Leva Miniatures and SHQ. HÄT are working on a "75", with caisson and horses, and it will come in both US and French variants.