WASHINGTON -- America's entry into World War I began with a year-long buildup beginning in April 1917. By late spring and early summer of 1918, that buildup was nearly complete.In response, the Germans launched a series of offensives, desperate to defeat the French, British and other allies. But ultimately, they would be overwhelmed with the addition of fresh American troops and firepower, according to Brian F. Neumann, a historian at the Center of Military History who compiled the pamphlet: "The U.S. Army in the World War I Era."One of the final German pushes occurred in the early morning hours of July 15, 1918, in the Champagne-Marne area of northern France, where German assault troops and artillery pounded the U.S. 3rd Division lines.The weight of the attack came against Col. Edmund Butts' 30th Infantry and Col. Ulysses Grant McAlexander's 38th Infantry. After heavy fighting in the morning, when the 30th Infantry "inflicted horrendous casualties" on the Germans, Butts' men were forced back to a line along the hills where they stopped the Germans.Elsewhere, five miles beyond the Marne River, McAlexander faced a more precarious position when the adjacent French division hastily retreated, leaving the 38th Infantry's right flank exposed, Neumann said.Turning some of the regiment to defend that flank, McAlexander also had to deal with a penetration of his main line. Although fighting on three sides, the riflemen and machine gunners of the 38th Infantry held their ground, earning the sobriquet "Rock of the Marne."The 3rd Infantry Division is still known by that moniker, and its Soldiers are proud of the heritage that inspired it.By the end of that July 15th day, the 3rd Division had stopped the German attack.Together, the 30th Infantry and 38th Infantry had defeated six regiments from two German divisions. One German 1,700-man regiment was so badly cut up that the German leaders could only find 150 survivors by nightfall, Neumann noted.Bad news also mixed with good that day. Four rifle companies of the 28th Division from the Pennsylvania National Guard had been attached to a French division to the east of the 38th Infantry. When the French retreated, they neglected to inform the Pennsylvanians, and the riflemen became surrounded. Most of them were killed or captured; only a few fought their way to the south to rejoin their parent division.Heavy fighting involving U.S. forces occurred near Paris in mid-to-late July, in what became known as the Aisne-Marne Campaign.By the first week of August, the U.S. Army's I Corps and III Corps had successfully wrapped up that campaign, removing the threat against the French capital and liberating several important railroads for allied use. That effort also eliminated the German high command's plans for another offensive against the British in Flanders."More important, the campaign effectively seized the initiative from the Germans and gave it to [French supreme allied commander, Gen. Ferdinand] Foch and his national commanders. The chance had passed for Germany to defeat Britain and France before the United States could intervene in force," Neumann said.The leader of the American Expeditionary Force, Gen. John Pershing, finally got his chance to command a large American-led campaign that included many French soldiers. The campaign in northern France, known as the St. Mihiel Offensive, lasted Sept. 12 to 16. Up until that time, U.S. units were used mainly in a piecemeal fashion.Firepower included over 3,000 artillery pieces, 1,400 planes and 267 tanks, mostly supplied by the French and British, but manned to a large extent by Americans, Neumann said.Pershing, at the suggestion of Gen. Henri-Philippe Pétain, commander of French forces, developed an elaborate scheme to deceive the Germans into thinking that the first blow would come to the south near Belfort on Sept. 12.French and U.S. forces under Pershing's leadership executed a four-hour long artillery bombardment against the German lines, an action commonly considered a prelude to attack by infantry and cavalry forces, Neumann noted.The scheme worked well enough to get the Germans to move three divisions into that sector, while allied forces, led by both I Corps and IV Corps infantrymen and tankers, began their attack in other more vulnerable areas."The Germans put up a determined defense long enough to retreat in good order," Neumann noted.On the afternoon of Sept. 12, Pershing learned that columns of Germans were retreating on roads from Vigneulles. The general urged both the 1st and 26th Divisions to continue their attacks through the night to press their advantage. The 1st Division was under IV Corps and the 26th Division came under V Corps.The 26th Division moved quickly throughout the night, capturing the strategic town of Vigneulles by 2:30 a.m., Sept. 13. The 1st Division then linked up with them, securing nearly all of their objectives, he said.In two days the U.S. Soldiers suffered some 7,000 casualties, while inflicting 17,000 on the German defenders.By Sept. 15, the St. Mihiel Offensive was successfully concluded. This operation paved the way for further offensives that would doom the German army in the coming months, Neumann said.Neumann added that the offensive gave Pershing and his staff "experience in directing a battle of several corps, supported by tanks and aircraft."Such an operation today is referred to as combined arms maneuver. But back then, it was a new approach to fighting.