45-mm anti-tank gun 19-K

The "Sorokapyatka" -- a 45mm Soviet anti-tank gun. It represents an evolution from 37-mm anti-tank gun known as the 1Q 1931 -- a licensed version of the German 37-mm PaK 35/36, but with a 45 mm barrel. At the time it was the most powerful anti-tank gun in the world. It was also adapted to be mounted on tanks. 

Thanks to its semi-automatic firing, improved sighting, mounting panel, and other advances, the "Sorokapyatka" met all the requirements of the time. By the beginning of the Great Patriotic War, the gun was the basis of anti-tank artillery.