When coordinated with the advancing infantry units, a creeping barrage of artillery shells provided the best chances for the survival of infantry soldiers. Designed to destroy both enemy positions and obstacles such as barbed wire and to provide cover in the form of smoke, the artillery battery was a key element in world war one trench warfare. As the war progressed the tactics for deploying artillery bombardments became increasingly sophisticated and, as a consequence, more deadly for the opposing side. Because battery units were, by necessity, within range of the enemy's guns, soldiers working in these units remained at permanent risk of being shelled themselves.