Fighting armor with infantry - the T-Gewehr

Even early in the World War, armor-piercing ammunition was developed for rifles to help defeat trench armor. The Mark I and Mark II were somewhat vulnerable to the 7.92x57mm steel-cored K bullet, but the Mark IV was essentially impervious. Thus, the Germans created a rifle around a 13.2x92mm steel-cored round that had been in development for the Maxim machinegun.

The first "modern" tank - the Renault FT

The Renault FT was the first tank that looked like what modern readers will consider a tank - an armored chassis with a rotating turret on top containing the main armament. The design was done by the Societe des Automobiles Renault, who had declined Colonel Estienne's original request to produce an armored vehicle based on the Holt tractor (the Colonel would move on to the Schneider company that produced the CA1). After Colonel Estienne approached Louis Renault again, Renault agreed to produce an armored vehicle, but to his design.