After several months of an aggressive German offensive on the Western Front during the spring and early summer of 1918, the Allies begin their counterattack, including an assault on June 10, 1918, by four French and two American divisions on German lines near the town of Antheuil-Portes in central France, some 45 miles from Paris.
Code-breaking by French intelligence at the beginning of June 1918 had allowed the Allies to prepare for a German attack in France that was to begin at midnight on June 7. The French launched their own massive artillery bombardment some ten minutes earlier, catching the Germans while they were still preparing for the attack. The Germans countered with an even stronger assault, firing 250,000 rounds of poison gas—including mustard, phosgene and diphenyl-chlorarsine—into the French trenches, incapacitating some 4,000 French soldiers and killing 32.
After three days of battle, the Germans had forced the French back to Antheuil-Portes. Winston Churchill, in Paris at the time coordinating Allied munitions, wrote to his wife on June 10 that "If the French cannot hold [the Germans] back on this sector, it is not easy to see what the next step on our part should be." The following day, four French and two American divisions launched a counterattack aided by significant air support as well as over 150 tanks. They successfully pushed the Germans back from Antheuil, taking more than a thousand German prisoners. A German attack west of Soissons on June 12 made negligible gains, and German Chief of Staff Erich Ludendorff called off the offensive that same day. The Allies continued their push, however, beginning a change of momentum that would gain force throughout the summer of 1918 and the final months of World War I.