Operation Michael, which marked the first sizeable German offensive against Allied positions on the Western Front in more than a year, began on March 21, 1918, with a five-hour-long bombardment of Allied positions near the Somme River from more than 9,000 pieces of German artillery, in the face of which the poorly prepared British 5th Army was rapidly overwhelmed and forced into retreat. For a week, the Germans pushed toward Paris, shelling the city from a distance of 80 miles with their “Big Bertha” cannons; by March 25, they had crossed the Somme and broken through the Allied lines. Hampered by a lack of supplies and cavalry, as well as hardening Allied defenses, German troops became exhausted, and by the end of March the Allies had halted their advance. On April 2, U.S. General John J. Pershing sent several thousand fresh American troops down into the trenches to fight alongside the British and French. It was the first major deployment of U.S. troops in World War I.
By April 5, when Ludendorff shut down the attacks, Operation Michael had produced the biggest gains of territory on the Western Front by either side since 1914. The Germans had advanced almost 40 miles, inflicted some 200,000 casualties and captured 70,000 prisoners and more than 1,000 Allied guns. The costs of battle were high, however: Germans suffered nearly as many casualties as their enemies and lacked the fresh reserves and supplies the Allies enjoyed following the American entrance into the war. Still, Ludendorff would launch four more similar operations that spring of 1918, as the Germans staked everything on a last, desperate offensive on the Western Front.