April 15 – American Ambulance Field Service is recognized within the French Army. Before and after this date American men and women volunteer to assist the wounded of France, Britain and Belgium in the war. Individual Americans had been serving as volunteers in France and elsewhere since 1914.
May 7 – The ocean liner RMS Lusitania is sunk by a submarine of the Imperial German Navy causing the death of nearly 1200 passengers and crew, among them 128 Americans.
April 16 – The Lafayette Escadrille is established. A French aviation unit largely made up of pilots from the United States. They, and those of the Lafayette Flying Corps, fly as combat pilots for France before the United States enters the war. Other Americans also fly in other Allied air services.
November 7 – President Wilson is reelected.
February 3 - United States severs diplomatic relations with Germany and President Wilson cites unrestricted submarine warfare as a threat to freedom of the seas.
March 1 - The United States is offered information concerning the Zimmerman Telegram suggesting Germany would support Mexico regaining American territory for joining an alliance against the United States.
April 2 to 6 – President Wilson demands, and the U.S. Senate approves a Declaration of War against Germany.
May 26 – General John J. Pershing is appointed Commander in Chief of the American Expeditionary Force (AE.F.).
May 18 – The Selective Service Act is enacted to allow conscription of American men for military service.
June 13 – General Pershing lands in France.
June 25 – The first American units land in France. United States Army stevedores of a segregated African American unit disembark and begin to unload materiel and equipment. They are followed shortly by combat units of the First Expeditionary Division, later designated the 1st Infantry Division.
July 4 – The 16th United States Infantry parades in Paris and the grave of Revolutionary War hero the Marquis de Lafayette is honored by an American military delegation.
July 14 – Louis Ganella, the Medical Corps is the first serving American Soldier to be wounded by enemy action while with British forces near Arras.
September 4 – First AEF killed by the enemy. Four American soldiers are killed at work in an English military hospital at Dannes – Camiers by German night bombing.
September 5 – The 11th Engineer Regiment is the first American unit to suffer casualties in operations at the front from shelling near Gouzeaucourt.
November 2 -First American Soldiers killed in action. Three soldiers of the U.S. 1st Infantry Division are killed during a German trench raid on their position at Bathelemont.
November 7 – The Supreme War Council is established at Versailles as an organizing body unifying the efforts of the Allies. Initial military representatives include the following;
•General Ferdinand Foch, France
•General Tasker Bliss, United States
•Lieutenant General Sir Henry Wilson,Great Britain
•Lieutenant General Luigi Cadorna, Italy
November 30 - The first large American unit in direct combat with the enemy. The American 11th, 12th, and 14th Engineer Regiments work near Gouzeaucourt is interrupted by a German counter attack. Though unarmed they obtain weapons and join English troops fighting and digging in under fire.
December 17th - The United States Declares War on Austria-Hungary.
January 8 – President Wilson promulgates the “Fourteen Points” as a plan for a just peace.
March 3 – Russia declares a separate peace with Germany under the Treaty of Brest Litovsk.
March 18 – The first report of Influenza at Camp Funston, a center of mobilization in Kansas. The pandemic will kill between 20 and 30 million worldwide.
March 31 – In an effort to conserve food and fuel and other materials the United States enacts “Daylight Savings”. It is a nationwide one hour adjustment of time that will be followed by Canada the following month.
April 8 – The 369th Infantry Regiment, Harlem Hellfighters, of the 93rd Infantry Division (Colored) begins to serve in the front lines with the French Army. The other regiments of the 93rd, the 370th Black Devils, and the 371st and 372nd Red Hand are all brigaded with larger French formations until fighting ends. They serve with distinction.
April 9 – German forces attack along the Lys River seizing Armentieres, Mount Kemmel and heights south of Ypres over the next two weeks. This causes a crisis in Allied Command but the front stabilizes. The American 16th Engineer Regiment, 1st Gas Regiment, and 28th Aero Squadron are committed to the defense.
May 27 – The German Army attacks along the Aisne River between Soissons and Rheims. The offensive takes Soissons and drives as deep as 30 miles to the Marne River where it encountered supply difficulties and stiffening Allied resistance. They are stopped at the Marne crossing at Chateau Thierry by the 3rd Infantry Division and in the area around Lucy le Bocage and Belleau Wood by the 2nd Infantry Division.
May 28 – American troops of the First Infantry Divisionre-take and hold the village of Cantigny against repeated counter attacks.
June 6 – American Soldiers and Marines of the 2nd Infantry Division counter attack German troops at Belleau Wood with support from the French Army. Heavy fighting continues there for two weeks across fire swept open fields and through densely thicketed woods.June 8 – The United States Navy begins laying the “North Sea Mine Barage”, over 56,000 sea mines in a three hundred mile long anti-submarine minefield between Scotland and Norway.
July 15 – The German army attacks on a seventy mile front from Chateau Thierry to Rheims and east to Navarin Farm. Rheims holds. To the east intelligence work and aggressive defenders including the U.S. 42nd “Rainbow” Division hobbles the attack. Southwest of Rheims the American 3rd Infantry Division earns the title “rock of the Marne” for defending under severe bombardment and repeated infantry attacks. The American 26th and 28th divisions, and the 369th Infantry Regiment take part in the fighting.
July 18 – The Allied Aisne Marne Campaign opens surprising the Germans who cease their attacks near Rheims. The 5th, 6th, 9th and 10th French armies, reinforced by eight American infantry divisions begin an offensive to eject the German Army from south of the Aisne and Vesle River lines.
August 8 – The British 4th Army, in cooperation with the French First Army open an offensive on the Somme, from the area of Amiens. The British 3rd Army joins in late August. Some German units collapse and the three armies advance until the end of fighting in November. The Australian and Canadian Corps are heavily engaged and accompanied by the American 33rd “Illinois” and the 80th “Blue Ridge” Infantry Divisions early in operations. These divisions are then withdrawn to join other American units further south.
August 10 – The United States First Army is established at Le Ferte-sous-Jouarre, France. It includes the American I, IV, V Corps and the French II (Colonial) Corps.
September 12 - The St. Mihiel Offensive begins. The United States 1st Army conducts attacks with Allied forces through September 16th. They push the German Army back 16 miles to the fortified Hindenburg Line hastening a planned retreat. It is the first use of tanks in combat by American forces, and commanded by George S. Patton. Brigadier General “Billy” Mitchell commands nearly 1500 warplanes supporting the offensive, an early massed use of aircraft. It is a competently executed large scale operation establishing a new frontline from Haudiomont to Pont-a-Mouson.
September 12 – American preparations are under way for the Meuse-Argonne Offensive under logistical control of then-Colonel George C. Marshall. In three weeks the A.E.F. repositions roughly one million men with supplies and materiel. Typically units move sixty miles by night, to face a different front from Vacherauville through Bouruiles to Vienne-le-Chateau. The I, V, and III United States Army Corps fall in behind trenches occupied by the French to conceal the American presence.
September 23 – General Pershing praises the Services of Supply who, commanded from Tours, provide the A.E.F. food, weapons, and materiel.
September 24 - The American 27th and 30th “Old Hickory” Infantry Divisions take part in the breaching of the heavily fortified Hindenburg Line of defenses between the 24th and 30th of September passing through Bony and Bellicourt. They remain under British command for the remainder of the war.
September 26 – The Meuse-Argonne Offensive opens with coordination between the American 1st Army and the French 4th and 5th armies. American troops advance from their lines to the Northeast through successive lines of German strongpoints with the aid of French Tanks, Aircraft, and Artillery.
October 2 – The “Lost Battalion”, six companies of 308th Infantry Regiment and detachments of the 306th Machine Gun Battalion become isolated capturing an objective near Charlevaux Mill. After reinforcement from a company of the 307th Infantry Regiment they are surrounded and attacked by German forces until October 7th. They are relieved by fellow units of the 77th Infantry Division.
October 6 – The German Chancellor offers terms for an armistice. The request is rejected by President Wilson.
October 8 – Private Alvin York earns the Congressional Medal of Honor. South of Cornay on the east side of the Argonne Forest Private York is part of a patrol of the 82nd Division attacking machine gun nests. After taking some prisoners their leaders become casualties. York takes command almost singlehandedly fighting off enemy attacks and capturing more Germans. He leads the patrol back to their unit with 132 prisoners. Though Alvin York’s story is famous there are many other acts of heroism in the ranks of the American Forces.
October 12 – The 2nd United States Army is created under General Bullard. As American and French forces continue the Meuse-Argonne offensive the A.E.F. reorganizes. General Pershing, retaining overall control, cedes command of the 1st Army to General Ligget
November 1 - Meuse Argonne Offensive is renewed under General Ligget’s command. They break through German lines north of Bouzancy and their capture of Boult-en-Bois allows the French 4th Army to advance across the Aisne.
November 6 - The American 1st Army advances to the gates of Sedan and its artillery closes the vital railroad supply line behind the German front.
November 8 – German delegates arrive at Compiegne to receive Allied terms for an armistice.
November 9 – Kaiser Wilhelm of Germany abdicates.
November 11 – American forces continue to attack and fighting ceases only after the signing of the armistice by the German and Allied representatives at Compiegne.
December 1 – Allied troops move up to the Rhine to take up occupation positions.
December 14 – President Wilson arrives in Paris.
January 4 – Peace Conference convenes in Paris.
JUNE 28 – Germany, the United States, and the Allied Powers sign Treaty of Versailles, the peace treaty that ends World War One.
July 9 – Germany Ratifies the Treaty of Versailles.
July 10 – The United States Senate receives the Treaty of Versailles from President Wilson and begins to debate it.
July 14 – Americans join with other Allied armed forces in a great victory parade in Paris.
November 19 – The United States Senate rejects the Treaty of Versailles.