The Regiment was then billetted at Bulligny, Bagneux, and Crezilles, with Regimental Headquarters at Bulligny. On 30 August, Col. Stuart took over command of the Regiment. The time until 1 September was used for drills and manoeuvres in preparation for the St. Mihiel Attack. On 1 September the Regiment proceeded independently by trucks, starting about 10:00 P.M. to the Bois de Minorville where the Regiment was held as Corps Reserve. Until 9 September the Regiment remained in the Bois de Minorville, keeping under cover and with a little drill in keeping liaison and in passing through thick woods in combat formation. On 9 September they marched via Minorville, Novian-aux-Pres to the Bois Dit-le-Rays, bivouacing on the Western side of the road running north to Limey from St. Jean. Movement began at dark in the following order: Third Battalion, First, and Second. The Second Battalion took up the support position, relieving other divisional troops. On 11 September, immediately after dark, the Regiment moved into the old French trench system on a front extending about one kilometer East from Limey in order: Third Battalion, First, and Second, with attached machine gun companies. Reconnaissance had been made by the battalion commanders; but the darkness and the character of the trench system, deep mud, and the fact that the whole Brigade, including gas and flame and engineer outfits, used the Boyau Hagemont as their route, made it a very difficult and long procedure. The Boche artillery did not fire. The "H" hour was not given out by the commanding officer until the elements had all taken position. At 1:00 A.M., 12 September, our artillery started in its preparatory fire on the enemy trenches, gradually increasing until 4:00 o'clock. Gas and flame units joined in on the bombardment, making great fountains of molten metal, gas and smoke, just preceding the jump-off, which was made promptly at 5:30. All battalions climbed out of the trenches, formed as they advanced, and after a delay of about five minutes, caused by failure of our own barrage to lift, moved forward on the German trenches from Remanauville on the East to Promenade-des-Moines on the West. Direction of the attack magnetic North. No real resistance was encountered in the enemy trenches, and as artillery fire was only spasmodic, troops of the Fifth Division on our right, and the Twenty-Third Infantry on our left, were advancing in perfect order. In and around the Bois du Four machine gun nests were met and overcome, and the pocket to the West toward Bois de L'Eveque finally cleared. The intermediate objective, the northern edge of the Bois de Four, was passed at about 7:00 A M. without halt, the Third Battalion continuing to lead. There was some loss and disorganization from enemy artillery, but the advance continued without interruption or any stubborn resistance to the line of the first phase, the northern edge of the Bois d'Heiche. The gradual brodening [sic] of the front assigned this Regiment, from one kilometer at the start to two and a half kilometers at Thiaucourt, caused a gradual drifting to the left; and from the first phase it was necessary to let both First and Second battalions pass through the Third Battalion, which followed in support.

The Second Battalion, commanded by Major George C. Bowen, was on the right sector. The First Battalion, commanded by Major Joseph F. Hodgson was on the left. The Third Battalion, commanded by Major Robert L. Denig, was in support. The army objective, or second day's objective was reached at 1:10 P, M. In order to maintain connection to the left, as ordered, the First Battalion extended over into the sector of the Twenty-Thrid Infantry, crossing the Rupt du Mad and capturing the heights dominating Thiaucourt, where it dug in along the camouflaged roads from a point about one kilometer directly North of Thiaucourt in a Northeasterly direction toward Jaulny, for five hundred meters; thence down steep slopes to second railroad bridge northeast of Thiaucourt in the Bois du Fay [sic Fey], occupied by the Second Battalion. In the afternoon it was reported that small detachments of the enemy were sifting into Jaulny. At 5:00 P. M. the First Battalion line was attacked with strong machine gun fire from the slopes Southwest of Jaulny, and by artillery placed in the Bois du Rupt. No artillery support was received and ammunition for the machine guns was short. A slow withdrawal was made behind the crest, and the Boche attack was caught as it was getting under way by friendly artillery coming into action and by a quick advance of our troops over the crest, which dispersed the enemy. At 7:00 P. M. a half hearted counterattack came from directly South in the Bois Blainchamp, supported by a battery of 88's in the Bois du Bonvaux against the line from Jaulny to the Bois du Bonvaux. This counter-attack was repulsed with small loss by the Second Battalion. Patrols sent out one kilometer in advance of the entire front located no enemy in force, though one prisoner stated that his Regiment, with one battery, had been hurried from Metz, and had been put in the Bois du Jaulny, but had left without attacking.

The estimated number of prisoners taken by the Regiment was 1600, of which the Third Battalion sent in approximately 1000. Property captured: Camps, or "Lagers" as follows : Fourwald, Pioneer, Saulswald, Brotzau, Bertram, Hamburger, Divisional Pioneer Park, Kriegshaus, Pioneer Lager, Minenwerfer Lager, Bayern, Bagagewaeldchen, Luther Lager No. 1, Luther Lager No. 2, and Feits Lager. Seventy-six guns, including one 57 mm, forty-two 77 mm, eight 88 mm, six 105 mm, nineteen 155's, twenty-three howitzers and minenwerfers; one hospital at Jaulny with large supplies of medical stores; one hospital train; one narrow gauge railroad with three engines and fifty cars; several ammunition store houses; machine guns; small arms in great quantities; two motor ambulances; one signal wagon complete and Thirty-Six horses. The losses were: Killed, two officers and forty-eight men; Wounded, four officers and two hundred and ninety-nine men.

On 13 September the lines were extended to include Jaulny, which had been taken the day before, but not held because of inability to inform all American artillery. During the afternoon there were some appearances of weak counterattacks from the Bois du Bonvaux, South, toward Col. Malone's Brigade of the Fifth Division. But as liaison had not been established, since army orders were that all elements should secure liaison to their left, no attention was paid until evening, when, in response to frantic appeals by wireless for help, directions from General Ely were received to co-operate. The Ninth Infantry was brought to the alert, standing to, to assist. The right flank of the Regiment was exposed, one company of the First Battalion extending the flank, the Third Battalion was faced East in support, and officer patrols were sent to investigate. Nothing materialized of this scare. Col. Malone's call for protective barrages from his own artillery brougth [sic] down fire on both the Second Battalion and the Fifth Marines, in rear, by short firing of the Twentith [sic Twelth] Field Artillery, which was only stopped after great difficulty.

Shortly after midnight of 14—15 September, the Fifth Regiment of Marines which was in support behind Bois du Fay, relieved the Ninth, and the Regiment was brought back to assemble in the ravine running from the Rupt du Mad second railroad bridge to the Bois d'Heiche. There was great aerial activity throughout this engagement, both American and Boche planes dropping in the regimental area. Our artillery barrage during the advance was well executed, and with the exception of one gun on the extreme left of the regimental front, which was discovered early in the attack, there was no short firing. The artillery of the Fifth Division on the right repeatedly shelled our support and the Fifth Marine areas and was only stopped after several repetitions. The Engineers were of assistance in wire destruction.