I left off last month pointing out the situations that forced the Americans to adopt foreign artillery types upon entering World War I. The best known of these foreign types was the French Canon de 75 modèle 1897 – often known simply as “The French Seventy-Five” or “Soixante-quinze” in the native tongue.
The Model 1897 is often cited as a “revolutionary” weapon. In reality it was more a case of evolution at the intersection of several development threads. Following the “butt-whipping” during the Franco-Prussian War (1870-71), the French adopted a program to improve field artillery. Through the following two decades several enabling technologies matured to levels to allow practical application. To name a few – smokeless powder propellant, breech-loading mechanisms (recall the breech block discussion), fixed ammunition, rifled steel gun tubes, all metal gun carriages, and recoil dampening mechanisms.
Recounting each of these development threads would be lengthy, and resemble some tome on artillery development. Let me instead walk through some of the particulars using a surviving example, at the USMC Museum.
First the breech. The French used a Nordenfelt rotating threaded breech block. Unlike the hinged interrupted-screw breech blocks we discussed earlier, the M1897 breech turned within the breech housing.
Rotating the handle from the lower right side to the upper left side exposed the breech of the gun tube, through the slot in the breech block. That slot became a feed chute for the loader. Rotating the handle back to the right engaged the screws, locking the block and closing the breech. Notice the lanyard leading up the rotating arm to the hammer.
The gun incorporated a lockout to ensure the block remained locked until the gun fired, or the gunner manually pulled a release catch. This ensured, in the rush of combat, the gunner didn’t open the breech on a hang-fire. The breech assembly also featured an extractor to push out the spent cartridge case.
As mentioned above, the M1897 fired fixed ammunition with brass shell cases. The case helped seal the breech. The 75mm fired two basic projectiles – a high-explosive shell or shrapnel.
The barrel of the gun was a “built up” variety. The main tube was steel. But over that were built up layers to provide strength over the breech end – not unlike some of the old Civil War era guns. This gave the tube profile two steps back towards the breech.
The recoil mechanism sat under the barrel in a protected housing, making examination difficult on a working model. The best diagram I’ve ever seen of the setup is from a 1933 Army manual:
Still somewhat incomprehensible. So here’s the cartoon version:
When the gun fired and recoiled, the piston in the upper tube of the hydro-pneumatic system compressed the oil into the lower tube. In the lower tube a floating piston then compressed the gas on the other end. As recoil force subsided, the gas pressed back against the floating piston forcing oil back into the upper tube. The upper piston then moved forward, thus returning the gun barrel to the firing position. Um.. simple… except for the very fine tolerances required for all the working parts.
This setup allowed the gun to recoil several feet back. Because of the weights involved, the muzzle of the gun tended to tip during recoil and could damage the carriage. To prevent that, a set of rollers attached below the muzzle engaged the recoil rails – giving the 75mm a distinctive profile.
Another component of the recoil system, often overlooked, is the trail spade.
Going into action, the crew would tip the trail up and let it fall. The trail sank in a few inches, even on hard ground. After the first round fired, the trail dug in sufficiently to stabilize the gun.
Another overlooked part of the system is the “abatage” or shoes under the wheels. At the same time the crew tipped the trail up, they would drop the shoes under the wheels. Notice the shoes locked in place here:
But for all the advanced nature of the carriage, the French 75 retained the straight “stock” carriage arrangement and wooden wheels of older field guns. The stock limited gun elevation. The wooden wheels were not so much a limitation as horses still pulled the gun and limber.
I would call attention to the data plate on the 75 at the museum:
If you look close, you see Willys-Overland Co. made this piece. I think you know more about Willys-Overland’s World War II products.
Sighting arrangements for the French 75 were on the left side of the gun.
With only six degrees of traverse and eighteen of elevation, the gunner had a little to work with. The important part is that brass sight allowed the gunner to use aiming stakes for referencing indirect fire. Not as good as panoramic sights (as was used on the US M1902 3inch gun), still an advance on old iron sights.
The whole setup worked rather well in action. Here’s a video with some clips showing the gun in action:
Notice about 10 seconds in, the crews tipping the guns to bury the spade. A good crew fired a round every two seconds.
So all in all a good weapon, right?
Well, there is some room for debate. The French 75 was two decades old by 1917 and surpassed by newer weapons. Arguably the American M1902 3-inch was a better gun in some respects. The same goes for the British 18-pdr gun, already in production at American factories. But, the American Army wanted compatibility – both as a gesture to the Europeans and to reduce shipping requirements. So the French 75 it was.
To meet immediate needs, the American Expeditionary Force purchased 600 guns directly from French stocks. The War Department had high hopes for domestic production of the French 75. But just as the M1916 story is an example of project development gone horribly wrong, the story of the M1897 is a story of production management gone bad. As such, it deserves treatment in the next post.