Trench warfare
Trench warfare has become archetypically associated with the First World War of 1914–1918, when the Race to the Sea rapidly expanded trench use on the Western Front starting in September 1914. By the end of October 1914 the whole front in Belgium and France had solidified into lines of trenches, which lasted until the last weeks of the war. Mass infantry assaults were futile in the face of artillery fire as well as rapid rifle and machine-gun fire. Both sides concentrated on breaking up enemy attacks and on protecting their own troops by digging deep into the ground. Trench warfare also took place on other fronts, including in Italy and at Gallipoli.
Rocket-propelled grenade
The static nature of trench warfare in World War I encouraged the use of shielded defenses, even including personal armor, that were impenetrable by standard rifle ammunition. This led to some isolated experiments with higher caliber rifles, similar to elephant guns, using armor-piercing ammunition. The very first tanks, the British Mark I, could be penetrated by these weapons under the right conditions. Mark IV tanks, however, had slightly thicker armor. In response, the German rushed to create an upgraded version of these early anti-armor rifles, the Tankgewehr M1918, the first anti-tank rifle. In the inter-war years, tank armor continued to increase overall, to the point that anti-tank rifles could no longer be effective against anything but light tanks; any rifle made powerful enough for heavier tanks would exceed the ability of a soldier to carry and fire the weapon.