The legendary 88mm artillery piece.  Originally for anti aircraft use, but was found to be a devastating anti tank weapon and all purpose gun.  It was first used in the Spanish Civil War, but was eventually deployed in every branch of the German military, serving on all fronts.

The 88mm

German gunners posing with a 50-mm anti-tank gun PaK 38. - When the Germans faced Soviet tanks in 1941 during Operation Barbarossa, the Pak 38 was one of the few early guns capable of penetrating the 45 mm (1.8 in) armor of the T-34. 

50-mm PaK 38

German gunners of the 19th Panzer Division fire a 50-mm anti-tank gun PaK 38 at an enemy target somewhere on the Eastern Front.