47 mm Model 1931 anti-tank gun

The Royal Cannon Foundry 47mm anti-tank gun Model 1931 (French: 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 millimetres (1.9 in) caliber by the Belgian soldiers that used it.

Source: Wikipedia — 47 mm Model 1931 anti-tank gun (CC BY-SA 4.0)