Civil War Union Army Brevet Brigadier General. Born in Ireland, he immigrated to the United States in 1851, and worked as a civil engineer in Chicago, Illinois, eventually becoming secretary and chief surveyor for the Chicago Board of Insurance Underwriters. When the Civil War began he in enlisted in the Union Army, and was mustered in as a Private in Company A, 12th Illinois Volunteer Infantry in April 1861. Commissioned 2nd Lieutenant and Regimental Adjutant on May 3, 1861, he served with the unit was it occupied Cairo, Illinois. When the 12th Illinois' enlistment expired in August 1861, it was reorganized into a three-year enlistment regiment, and on August 1, 1861 Arthur Ducat was promoted to Captain and company commander. Advanced to Major on September 24, 1861, he was with the regiment during the November 1861 Belmont, Missouri campaign and in the capture of Forts Henry and Donalson on the Mississippi River in February 1862, where he was severely wounded and put of out field service for a number of months. Promoted to Lieutenant Colonel on April 1, 1862 for his gallantry at Fort Donelson, when he was recovered sufficiently he was assigned to the staff of Major General Edward O.C. Ord, serving in that duty through the September 1862 Battle of Iuka. After being briefly assigned as Chief of Staff for the Army of the Cumberland's XIV Corps, Army commander Major General William S. Rosecrans plucked him from that duty and assigned him to his staff as his Chief of Staff. Soon after though, the Chief of Staff position was given to Lieutenant Colonel Julius Garesche, and Colonel Ducat was assigned as Assistant Inspector General, a role he would serve in until his muster out on February 19, 1864. At the September 1863 Battle of Chickamauga he performed perhaps his most feted service when, as the defeated Union army was in a rout, he stopped many retreating soldiers with the headquarter's cavalry escort and fed them to the stand being made by Major General George Thomas on Snodgrass Hill. General Thomas's desperate stand after the Confederates smashed the Union forces through a gap that opened their center saved the Army of the Cumberland. On March 13, 1865 Colonel Ducat was brevetted Brigadier General, US Volunteers for "faithful service". After the war he returned to Chicago, serving in duel careers as an engineer and a fire insurance agent. After the Great Chicago Fire of 1871, he had a large influence on the creating and passing of new fire codes and laws designed to prevent such conflagration again. He passed away in 1896.