What military innovation was introduced on a large scale during World War I?

Tanks

Tanks, first introduced to the battlefield by the British in 1916 during the Battle of the Somme, represented a revolution in land warfare. Designed to break the deadlock of trench warfare, these steel behemoths made a significant impression with their imposing appearance and ability to cross difficult terrain. However, their initial impact was less due to their effectiveness in combat than to the terrifying psychological effect they had on enemy troops. The early models were notoriously unreliable and slow, but their mere presence could sow panic. Beyond their military contribution, tanks changed the perception of modern warfare, paving the way for continuous innovation in armored warfare and symbolizing the shift to increasingly mechanized conflicts.