The d5minant feature during the first eight months of 1918 was a series of ferocious German offensives. Empowered by the collapse of the enemy on the eastern front, Ludendorff was able to transfer the weight of his forces to the west. From March until July, Germany's armies struck the enemy lines, often with devastating effect. The German effort rested on the imaginative use of the classic tools of the war: men and guns. Superior use of artillery now combined with new infantry tactics. Specially trained assault units, for example, slipped around the enemy's defensive strongpoints to disrupt the rear. In its first appearance, against the British in Artois in March 19 1 8, the German advance brought apparently spectacular results. Nonetheless, the advantage remained in the weary hands of the defenders. German losses, even in victorious advances, were heavy; Allied leaders, both military and civilian, avoided panic; and under the weight of the crisis, all Allied forces were placed under a single leader, France's General Ferdinand Foch. Meanwhile, seeking a decisive kill, Ludendorff desperately shifted the weight of his efforts from one sector of the front to another. The arrival of American troops boosted Allied morale and correspondingly shook the German spirit, even though large numbers of the newcomers were not in the fight until the fall of the year.