America was in the thick of its biggest battle 100 years ago this fall.

The seven-week Meuse-Argonne campaign started Sept. 26, 1918 and lasted to the second the guns fell silent with the Armistice on Nov. 11.

The campaign involved 1.2 million American soldiers heavily supported by French troops, 1,000 aircraft and 400 tanks. It was the first time Americans faced the horrors of modern warfare — poison gas, hand grenades, flame-throwers, machine gun nests and strafing by German airplanes.

More than 26,000 American soldiers died during the battle and nearly 100,000 were wounded.

The Meuse-Argonne was a testing ground for a generation of American commanders who led the nation to victory in World War II. The roster includes Brigadier General Douglas MacArthur, Col. George C. Marshall, Lt. Col. George S. Patton and Capt. Harry S. Truman.

Two bona fide heroes emerged from the conflict — Cpl. Alvin York of Tennessee who killed 32 Germans and helped capture 132 others when he stormed some machine guns nests and Major Charles Whittlesey of the Lost Battalion.

Gen. John Pershing, the commander of the American Expeditionary Force, insisted on leading a separate army and not having it split up among French and British units. But the price of independence was the death of many American soldiers as their inexperienced commanders ordered headlong assaults against machine gun nests.

The Meuse-Argonne was the last big offensive on the western front during World War I. The Americans broke through the Hindenburg Line in several places and the Germans sued for peace as their allies collapsed under the strain of war.

Yet few Americans are aware of this largest battle in U.S. military history overshadowed as it is by Gettysburg and D-Day.

The Meuse-Argonne took its name from the Meuse River and Argonne Forest in the northeast corner of France. The battle was fought over difficult terrain for attack with the Germans entrenched in concrete bunkers on the heights above the Meuse. The advancing American soldiers had to deal with thick underbrush and ravines, shell holes and barbed wire. The weather was horrible that fall with cold rains making life miserable.

The battlefield was near two historic French towns – the fortress stronghold of Verdun that withstood a German siege in 1916, and Sedan where the Prussians trapped the army of Napoleon III in 1870.

My grandfather, George S. Swift, fought in the Meuse-Argonne as part of the 319th Infantry, 80th or Blue Ridge division. He had entered the Army one year before at Avalon, Pa., near Pittsburgh.

He wrote of Lt. Paris T. Carlisle dying in his arms after being hit by shell-fire.

Many notations in his diary deal with the everyday existence of a soldier, of being in the “dark woods” on a cold rainy night.

Sept. 30: “Our kitchen comes up and we get a meal for the first time from it in six days.”

Oct. 2: “Jerry shells all night and it is cold as can be.”

At the start of November, the Americans launched a new offensive to reach the critical German-held rail lines at Sedan.

As the battle continued, soldiers on both sides knew the end was near with reports of peace talks based on Woodrow Wilson’s Fourteen Points and revolution in Germany.

On Nov. 3, my grandfather noted: “More Peace talks. Armistice bulletin posted. But guns still booming.”

On Nov. 11 at the real Armistice was announced, he wrote “Bells ring and flags out. But who can believe it?”

The American Battle Monuments Commission held a centennial ceremony for the Meuse-Argonne campaign Sunday at the Meuse-Argonne American Cemetery in France. This is the final resting place for 14,247 soldiers, including nine Medal of Honor recipients.

The commission maintains the Pennsylvania Monument built in 1927 by the Commonwealth at Varennes, France. The monument underwent a needed restoration in 2015. – Robert Swift