Trench warfare
Trench warfare prevailed on the Western Front from late 1914 until the Germans launched their Spring Offensive on 21 March 1918. After the buildup of forces in 1915, the Western Front became a stalemated struggle between equals, to be decided by attrition. Frontal assaults, and their associated casualties, became inevitable because the continuous trench lines had no open flanks. Casualties of the defenders matched those of the attackers, as vast reserves were expended in costly counter-attacks or exposed to the attacker's massed artillery. There were periods in which rigid trench warfare broke down, such as during the Battle of the Somme, but the lines never moved very far. The war would be won by the side that was able to commit the last reserves to the Western Front.
Anti-tank warfare
Anti-tank warfare arose as a result of the need to develop technology and tactics to destroy tanks during World War I. Since the first tanks were developed by the Triple Entente in 1916 but not operated in battle until 1917, the first anti-tank weapons were developed by the German Empire. The first developed anti-tank weapon was a scaled-up bolt-action rifle, the Mauser 1918 T-Gewehr that fired a 13mm cartridge with a solid bullet that could penetrate the thin armor of tanks of the time and destroy the engine or ricochet inside killing occupants. Because tanks represent an enemy's greatest force projection on land, anti-tank warfare has been incorporated into the doctrine of nearly every combat service since. Most predominant anti-tank weapons at the start of World War II were the tank-mounted gun, anti-tank guns and anti-tank grenades used by the infantry as well as ground-attack aircraft.