At the end of the first training period the regiment marched on June 12 and 13 to Morvillars, where it entrained for Ligny en Barrois (Meuse). It then moved near the town of Bar-le-Duc in the department of the Meuse. Here it was declared fit for active service, and on June 21 it was placed on the front line in a quiet sector in the St. Mihiel district for fourteen days. Leaving for the Argonne on July 19, it was placed in the Verdun sector on the plateau of Gorgia and at Hermont and Mont des Allieux. At the last named place, on July 24, the first casualty in action took place when Private Robert M. Lee of machine-gun company No. 2 was killed. The only other operation except the usual routine work was the raid of a Stokes mortar platoon, commanded by Lt. Robert A. Wood, on August 4. This was in the sub-sector of Vauquois. Three hundred rounds of ammunition were fired, the object being to fill up the gaps of the artillery barrage. On August 15 the 370th was placed at the disposal of General Mangin, who was commander of the 10th Army and who ordered the regiment in reserve along the Curcq River. From this position it was taken on September 15 to the Soissons sector with the 59th Division in the area of Vauxaillon with the Ailette Canal and Alizy Château as its strong salients. The Third Battalion, commanded by Colonel Otis B. Duncan, succeeded in taking the southern boundary of the canal. Four rifle companies were detached with two French regiments and assisted in taking Mont des Singes. The fighting was severe. The 370th was usually in close support, but it also participated in several attacks, in all of which the objectives were gained. For the first time, on September 22, the regiment was given a full sector extending from L’Écluse to a point 300 meters west of the crossing of the Pinon Braucourt road. The First Battalion went into a position on the Oise-Aisne Canal and the Farm Guilliminet, the Second into a support position at Mont des Tombs and Les Tueries and the slopes west of Antioche Farm, and the third into reserve at Tincelle Farm. The headquarters company was stationed at Levilly and the supply company at Monte Couve. In the midst of the relief of the First and Second Battalions on the front line during the night of September 27, an attack was ordered at dawn. By the greatest effort the relief was completed and the Second Battalion, which was ordered to work, began offensive operations. These lasted three days. During the night, while the relief was being conducted, there was considerable mixing of units. It was difficult to maintain liaison and as a result one company advanced too far and a number of casualties resulted.