Bofors 37 mm The Bofors 37 mm gun was an anti - tank gun designed by Swedish manufacturer Bofors in the early 1930s . Licensed copies were produced in a number of countries . The gun was used by some European armies during World War II , mainly at the early stage of the war . Development history . The gun was initially designed by Swedish manufacturer Bofors , mainly for export purposes . The first prototype was built in 1932 ; the development process continued until 1934 . The Netherlands were the first to purchase the gun ( order for 12 pieces was placed in 1935 ) and were followed by many other countries . Licensed copies were produced Denmark , Finland , the Netherlands and Poland . The barrel was of monobloc type , with semi - automatic vertical sliding breech block and small muzzle brake . It was mounted on a split trail carriage which had suspension and metal wheels with rubber tires . To give the crew some protection from firearms and shell fragments , the gun was equipped with a 5 mm thick shield , with a folding lower plate . Employment history . The Bofors gun saw combat for the first time in Spanish Civil War , where it could easily pierce the armor of contemporary light tanks . The Polish guns were actively used during the German and Soviet invasion of Poland in 1939 . Wołyńska Cavalry Brigade equipped with the Bofors 37 mm antitank gun beat the German Panzer Division s in one of the first battles of the invasion ; the Battle of Mokra . At that time , the armored forces of the Wehrmacht consisted mainly of light Panzer I and Panzer II tanks , which were vulnerable to the Bofors gun . Early models of the Panzer III and Panzer IV could also be penetrated at ranges up to 500 m . After Poland was occupied , most of the guns fell into the hands of the German and Soviet armies . The weapon was proven obsolete by 1941 during the Operation Barbarossa . Even though only one Bofors AT - gun was in action in the Invasion of Denmark , it damaged two tanks , and shot the tracks of another tank , before its crew were either wounded or killed by a German tank destroyer which drove over the gun . The gun is now at the Tøjhusmuseet in Copenhagen . During the Winter War , the Finnish guns were successfully used against Soviet tanks such as T - 26 , T - 28 and BT . However in the Continuation War the gun was found to be ineffective against the T - 34 and KV and was relegated to an infantry support role . The gun was used to equip the British forces in North Africa , where it made up for the lack of the QF 2 - pounder anti - tank guns after the Fall of France . It was often carried " portee " on the back of a vehicle . Bofors guns were also employed in World War II by Germany , the Netherlands , Romania , Yugoslavia and USSR , but there are no detailed reports of their use . Summary . When it was introduced , the Bofors 37 mm anti - tank gun was an effective weapon , able to deal with contemporary tanks . Its performance , light weight and high rate of fire made it a popular anti - tank weapon in the pre - war Europe . However , introduction of better armored tanks early in World War II made the gun obsolete ( as it made obsolete other similarly performing weapons such as the German PaK 36 and the US 37mm M3 .