It was the French who made the best tank of the Great War, the FT-17; it was also the French who made the best gun, the Canon de 155 GPF. It was the brain child of Lieutenant-Colonel LJF Filloux, of the French artillery, a man who in many ways was an artillery pioneer. Already before the war had he been involved in projects aiming to improve different guns. His ideas for a new, long-range 155mm gun presented were however ignored before 1914, as there seemed to be no need for such a weapon – the famous 75mm mle 1897 field gun was said to fill all needs. This soon changed, and by 1916 Filloux could once again present his idea for a new gun. This time it was gratefully accepted, as the French army had requested a gun with a range of at least 16,000m, that could be towed in high speed, and that had a wide angle of traverse, enabling the gun to cover a wide target area.
The result was the prototype that – like the FT-17 Tank in its field – influenced most of the designs that were to follow. The Canon de 155 GPF (the GPF denoted “Grand Puissance Filloux”, “Grand Puissance” can be translated as “Very Powerful”) employed a long, slender 38-calibre barrel placed on a split-trail carriage. It was the first big gun to use such a trail. The only fore-runner had been the 75mm Deport Field Gun, and although this innovation had worked remarkably well, many were apprehensive about putting a powerful 155mm gun on such a special carriage. (One of the vehicles used to tow the 155 GPF was the Latil-TAR tractor.) Also, Fillioux gave the gun a suspension capable of being towed, not only fast on roads, but also across rough terrain.
By pulling the long barrel back (after disconnecting it from the recoil system) to a bracket on the joint trail legs on a limber, the GPF formed a well-balanced single load. For transport the gun was and run back to lock on, so spreading the weight. When emplaced the split-trail carriage formed a steady firing platform with a wide angle of traverse (60°), and a maximum elevation of 35 degrees. The breech mechanism was of the well-proven Schneider screw type. The gun had a variable recoil, giving a full recoil of 1.80m up to 10° of elevation, then shortening until at 28° and above it was 1.10m. The formidable elevation and traverse allowed a single gun to reach something like 206 square kilometres of ground. Overall the GPF was one of the best artillery designs of its day, and for long after, its range of 19,500m going far beyond the original 1916 requirement.
The GPF went into series production during 1917, and was used for the first time in August that year, in Flanders. When American troops arrived in France they immediately saw the value of the GPF and placed big orders to equip their own forces. The orders were so substantial that deliveries to the French army were affected, leading them to adopt the stopgap gun 155 mle 1918. After 1918 the US army adopted the GPF as the M1917 and M1918, and started producing their own. When WW2 started the GPF was still one of the best artillery pieces around. The French Army had some 450 of them. Poland also employed this gun. Most of the French GPFs were eagerly taken over by the Germans, who used them, among other places, in the Atlantic Wall. In the US a redesign of the GPF resulted in the formidable 155mm M1 “Long Tom” gun, perhaps the best heavy gun of WW2. And after the war the French took their experiences with the GPF and made the 155mm Mle 1950 Howitzer, that was used in many countries, including both Syria and Israel.