Thomas Sweeny was 13 years old when he immigrated to the United States from Ireland in 1833. In 1846, he enlisted as a second lieutenant in the 2nd New York Volunteers, and fought under General Winfield Scott in Mexico, where he was wounded several times, including losing his right arm due to an injury sustained at the Battle of Churubusco. For his heroics, his fellow servicemen nicknamed him “Fighting Tom”. At the outbreak of the Civil War, Sweeny was in command of the St. Louis Arsenal. When Confederate sympathizers tried to seize it, he told them he would blow it up before he would ever surrender it. Sweeny went on to participate in the fighting at Wilson’s Creek, Fort Donelson, and at Shiloh, where he successfully defended a gap in the Union line, despite being shot twice in his remaining arm and once in one of his legs. At the Battle of Atlanta, Sweeny’s division intercepted John B. Hood’s flank attack. Sweeny’s corps commander, General Grenville Dodge, broke protocol and personally directed one of Sweeny’s brigades during the fight, which angered Sweeny and prompted him to fistfight Dodge with his one remaining arm. Sweeny received a court-martial but was acquitted. He mustered out of the volunteers in August 1865.