 The U.S. Navy adopted the Gatling gun during the war, where it was used on federal gunboats, but the U.S. Army did not formally adopt it for use until 1866.The first military execution in the war's western theater occurred on March 27, 1863, at Camp Burnside (Burnside Barracks).Robert Gay, a 27-year-old schoolteacher from Clay County, Indiana, was executed by a 20-man firing squad.