With the Battle of the Aisne grinding to a halt as trench warfare gradually set in, both the German and Allied commanders realised the dominance of the defensive, established by quick firing artillery and the machinegun, meaning that casualties in frontal attacks on a dug-in enemy were enormously heavy. Consequently, the armies sought to outflank the opposition by heading north in a set of manoeuvres known as the Race to the Sea. During this phase Field Marshal French insisted on redeploying the British Expeditionary Force to the Allied left, nearer the Chanel ports.