47 mm Model 1931 anti-tank gun

The Royal Cannon Foundry 47mm anti-tank gun Model 1931 (Canon anti-char de 47mm Fonderie Royale de Canons Modèle 1931, abbreviated to C.47 F.R.C. Mod.31) was an artillery piece developed in 1931 for the Belgian Army which saw widespread service in the Battle of Belgium in 1940. It was colloquially known as the "'Quat'sept," nicknamed after its 47 mm caliber by the Belgian soldiers that used it.

It was developed by the firm F.R.C., the Herstal-based Fonderie Royale de Canons, not to be confused with the French F.R.C.

Versions
There were two versions of the 47mm gun, each developed for a different situation: the Infantry version and the Light Troops version. The Infantry Version was furnished with heavier but more durable full-rubber tires. In contrast, the Light Troops version was equipped with pneumatic tires for greater road mobility. Both versions were capable of being incorporated into fixed defenses and bunkers for stationary purposes. One such example of this was in Belgium at the fortifications of the Albert Canal. They were also attached to Belgian combat vehicles of WWII as support weapons, such as the T-13 tank destroyer and the 'Canon antichar automoteur Vickers-Carden-Loyd Mk.VI'.

Performance
The 47mm anti-tank gun had an impressive performance compared to contemporary WW2 German or French designs – respectively the 3.7 cm Pak 36 and 25mm Hotchkiss anti-tank gun. In medium-range armor penetration, the Belgian model even outperformed the British Ordnance QF 2-pounder. For instance, armor-piercing rounds could penetrate 47 mm of armored steel at a range of 300 m. This type of damage was largely attributed to the heavy caliber design with a shell weight of 1.52 kg for the armor-piercing rounds.

However, this performance came at a price. With a total weight of 515 kg (not including ammunition or other equipment) the 47mm was a lot heavier than the German Pak 36 at 327 kg, 37 mm gun M3 at 912 lb or 37 mm Bofors at 370 kg, although the Soviet 45-mm was about the same at 560 kg while the 2-pdr was significantly heavier at 1795 lb. Despite its substantial mass, the 47mm was easier to conceal due to its relatively compact design. Repositioning of the Belgian anti-tank gun was aided by the Vickers Utility B armored tractors in the infantry divisions or the Ford Marmon Herrington armored tractors in the cavalry units.

Belgium
Over 750 47mm guns were in service in the Belgian army at the time of the German invasion in 1940. All active and first reserve infantry units, cavalry units, and units of the border guards were equipped with the gun, while the second reserve units had to make do with older anti-tank rifles. Every infantry regiment consisted of 3 battalions of rifle infantry and a single heavy arms battalion. This in turn consisted of three heavy weapon companies, one of which was equipped with 12 47mm guns. Given its good armor-penetrating capabilities, the 47mm could penetrate the armor of the German Panzer III and Panzer IV tanks from a range of over 500 m.

Germany
Several hundred 47mm guns were captured by the Germans after the battle of Belgium. The German designation for these captured guns was the 4.7 cm Pak 185(b). A few were installed in Atlantic Wall defenses in Belgium and the Channel Islands.

Hungary
Several of the 47mm guns captured by Germany were donated to Hungary in 1940-1. This donation was to make up for Hungary's lack of anti-tank guns during Operation Barbarossa. However, their use by the Hungarians was limited due to a lack of spare parts. Furthermore, the armor-penetrating capabilities of the guns had also been surpassed by Soviet advances in tank construction. Most of the captured guns were relegated to training duties instead.