Germany was the first country to produce a purpose-built antitank rifle, in response to the major Entente tank attack at Cambrai. The design was pretty simple, basically a scaled-up Mauser 98 with 4 locking lugs chambered for the massive 13.2mm TuF cartridge. It would perforate about 20mm of armor plate at 100m, which was nicely effective on WWI tanks. By the end of the war more than 15,000 1918 Tank Gewehr rifles had been made. Interestingly, a bunch of them ended up at Springfield Armory, where they were used in the development of the .50 BMG cartridge.