The early autumn of 1917 witnessed steady gains by the British and French forces co-operating in Flanders and to the South of the Belgian border along the western front. The artillery on both sides was constantly active, but with evident superiority on the part of the Allies. Repeated German attacks were repulsed in the Champagne and along the Meuse, while in the Ypres region the Allied troops made frequent gains in spite of the concrete defenses established by the enemy to strengthen their entrenched positions. Repeated successes of the Allies along the Chemin des Dames finally forced a German retreat along a fifteen-mile front which the Crown Prince had made strenuous efforts to hold. The Germans were compelled to retire because French victories on October 21-23 enabled French guns to enfilade the Ailette Valley behind the German positions, exposing the enemy to a series of disastrous flanking attacks and hampering the German communications. On October 30-31 the French bombarded the German lines vigorously. The enemy had already moved their artillery across the Ailette to a ridge north of the river. On the night of November 1 they completed their preparations for retreat and withdrew their infantry. French patrols approaching the German lines on the morning of November 2 were fired upon at first, but on renewing their reconnoissance soon after dawn found the German trenches empty. It was impossible for the Germans to keep their front line supplied with ammunition or food, the carriers of which were obliged to pass through a tornado of shells and machine gun bullets while crossing the Valley of the Ailette, where their every movement could be observed by the French. Eventually the position became untenable and the Germans retired during the night to the Northern side of the Ailette Valley. The best elements of the Crown Prince's army had sustained severe losses and were compelled to go to the rear to reconstitute their diminished ranks. The evacuated territory North of the crest of Chemin des Dames included several towns that had been pulverized by bombardment, and the retreat brought the important city of Laon within range of the French guns. The captures by the French in this sector from September 23 to November 1 included 12,000 prisoners, 200 heavy field guns, 220 trench mortars, and 720 machine guns. In ten days, from September 21 to 30, twenty-three German airplanes were destroyed and twenty-eight forced to descend badly damaged. THE FIRST AMERICAN CASUALTIES The first list of Americans killed and wounded in combat with the enemy reached Washington on October 17, in an official report from Rear Admiral Sims of an encounter between a German submarine and an American destroyer. One American sailor was killed and five sailors were wounded when the submarine torpedoed the destroyer Cassin on patrol duty in European waters. The destroyer was not sunk and after making a gallant fight reached a British port.