How did heavy artillery support attacks on trench systems during World War I?

During World War I, heavy artillery was essential for attempting to overcome entrenched enemy positions. Because soldiers had sought refuge underground to survive modern machine-gun fire, traditional infantry charges were often ineffective against fortified trench systems.12

To break these defenses, commanders employed massive concentrations of heavy artillery to bombard enemy lines with high explosives and toxic gases. These attacks were directed by forward observers, aircraft, and balloons to improve accuracy. Initially, these bombardments were often daylong or week-long affairs intended to destroy barbed wire and defensive dugouts before an infantry advance.13

However, these long bombardments often alerted the enemy, allowing them to move their main forces to safety. Later in the war, tactics evolved toward shorter, more intensive barrages that relied on mathematical calculations and weather reports for surprise, rather than firing registration rounds. Despite these efforts, the defensive power of deep, multi-layered trench systems—often reinforced with concrete pillboxes—frequently rendered even the best-organized artillery-supported attacks insufficient to achieve a decisive breakthrough.13