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.
Logistics in World War I
However, as the war ground down into static trench warfare it became easier for armies to support their troops with the use of the railway, especially for the artillery. This made the transportation of supplies easier and quicker to get from the factories to the front line. This did have problems of their own, as seen by the Shell Crisis of 1915. Where the stalemate of trench warfare took hold, special narrow gauge trench railways were built to extend the rail network to the front lines. The great size of the German Army proved too much for its railways to support except while immobile. Tactical successes like Operation Michael devolved into operational failures where logistics failed to keep up with the army's advance over shell-torn ground.