In July, the Germans launched an assault against the Allied line, known as the Second Battle of the Marne. A three-hour artillery pounding of the 3rd Division's position announced the beginning of the offensive. In the dark of night, boats ferried the first waves of troops from the German Seventh Army. In short order, French and American defenses closest to the southern flanks of the river crumbled and were overrun. The swarming enemy was so well established on the 3rd Division's right flank that its position should have been untenable. And exactly here stood McAlexander's 38th, beset from both sides. Apparently, McAlexander had expected just these developments. Without yielding his hold on the Marne embankment, McAlexander refused both flanks so that his regimental front stood like a horseshoe, one battalion forward, one on either side. Try as they would, the Germans could not move this rock in their midst. McAlexander's 38th held out, and maintained their position. Because of their steadfastness, McAlexander and his 38th Infantry Regiment became known from then on as the Rock of the Marne. The German offensive was halted by 18 July 1918. For his decisive action, Col. McAlexander received the Army Distinguished Service Medal.