Military actions designed to take control of enemy trenches were called attacks or offensives. Whereas an attack usually involved a division (16,000 men), an offensive was much larger and would use at least one corps. The main objective of an attack was to break the enemy line but an offensive was an attempt to hold any positions that were taken during the operation. This meant sustained fighting in forward positions and raised serious problems of supplying soldiers with ammunition, food and water.

Before attacks and offensives took place, heavy artillery was used to soften up the enemy trenches. At the offensive at the Somme in the summer of 1916 General Douglas Haig ordered an eight-day preliminary bombardment before sending 750,000 men (27 divisions) to attack the German trenches. The following year, Haig decided on a ten day bombardment during the offensive at Ypres (the Battle of Passchendaele). This barrage involved 3,000 guns firing 4,283,550 shells at the German defences.