The 2nd Maine was recalled into Federal Service on 18 June 1916, and served along the Mexico–United States border in Texas to guard against hostile raids. On 13 April 1917, elements of the 1st New Hampshire Volunteer Infantry were merged into the 2nd Maine to create the 103rd Infantry Regiment. The new regiment was placed in the 52nd Infantry Brigade (alongside the 104th Infantry Regiment) as part of the 26th Infantry Division, the "Yankee Division." The regiment served on the Western Front and was one of the first National Guard units in combat during the war. The 103rd served in the Champagne-Marne campaign where they had their first real taste of fighting, and went on to fight gallantly in the Aisne-Marne. The bloodied New Englanders continued the fight at the Battle of Saint-Mihiel, and in the momentous Meuse-Argonne Offensive, the largest and bloodiest operation of the war for the American Expeditionary Forces.