Bofors 57 mm m/54 anti-aircraft gun
The Bofors 57 mm m/54 (57 mm luftvärnsautomatkanon m/54 or 57 mm lvakan m/54) was a wheeled automatic anti-aircraft gun for land based use produced by Bofors and developed from the similar Bofors 57 mm m/50 naval artillery gun. The gun was developed in the 1950s and fielded by both the Belgian and Swedish military.
Source: Wikipedia — Bofors 57 mm m/54 anti-aircraft gun (CC BY-SA 4.0)