<P> The United States Navy sent a battleship group to Scapa Flow to join with the British Grand Fleet, destroyers to Queenstown, Ireland, and submarines to help guard convoys . Several regiments of U.S. Marines were also dispatched to France . The British and French wanted American units used to reinforce their troops already on the battle lines and not waste scarce shipping on bringing over supplies . General John J. Pershing, American Expeditionary Forces (AEF) commander, refused to break up American units to be used as filler material . As an exception, he did allow African - American combat regiments to be used in French divisions . The Harlem Hellfighters fought as part of the French 16th Division, and earned a unit Croix de Guerre for their actions at Château - Thierry, Belleau Wood, and Sechault . AEF doctrine called for the use of frontal assaults, which had long since been discarded by British Empire and French commanders due to the large loss of life that resulted . </P> <P> Ludendorff drew up plans (codenamed Operation Michael) for the 1918 offensive on the Western Front . The Spring Offensive sought to divide the British and French forces with a series of feints and advances . The German leadership hoped to end the war before significant U.S. forces arrived . The operation commenced on 21 March 1918, with an attack on British forces near Saint - Quentin . German forces achieved an unprecedented advance of 60 kilometres (37 mi). </P> <P> British and French trenches were penetrated using novel infiltration tactics, also named Hutier tactics, after General Oskar von Hutier, by specially trained units called stormtroopers . Previously, attacks had been characterised by long artillery bombardments and massed assaults . However, in the Spring Offensive of 1918, Ludendorff used artillery only briefly and infiltrated small groups of infantry at weak points . They attacked command and logistics areas and bypassed points of serious resistance . More heavily armed infantry then destroyed these isolated positions . This German success relied greatly on the element of surprise . </P> <P> The front moved to within 120 kilometres (75 mi) of Paris . Three heavy Krupp railway guns fired 183 shells on the capital, causing many Parisians to flee . The initial offensive was so successful that Kaiser Wilhelm II declared 24 March a national holiday . Many Germans thought victory was near . After heavy fighting, however, the offensive was halted . Lacking tanks or motorised artillery, the Germans were unable to consolidate their gains . The problems of re-supply were also exacerbated by increasing distances that now stretched over terrain that was shell - torn and often impassable to traffic . </P>

Where did the main fighting take place in ww1