John Trout Greble (January 19, 1834 – June 10, 1861) was an American military officer who served in the Union army during the American Civil War. He graduated from the United States Military Academy and served in the United States Army during the Third Seminole War. He was killed in action at the Battle of Big Bethel, and was the first Regular Army officer and graduate of the United States Military Academy killed in the American Civil War. He was assigned to the 2nd artillery, and stationed at Newport, Kentucky.[5] In September 1854 he was made second lieutenant and deployed to Tampa, Florida, where he served in the Third Seminole War for two years. He returned home on sick leave due to severe fever and resumed his duties at the beginning of 1856. He served as quartermaster and commissary until December 1856. He was promoted to first lieutenant on March 3, 1857. He was appointed acting assistant professor of geography, history, and ethics at the United States Military Academy, and served in that role until September 24, 1860.[6]

He was detailed for active duty at Fort Monroe in late 1860, and helped prevent its capture by Confederates. On May 26, 1861, he was sent to Newport News as master of ordnance, supervised the fortifications, and trained the volunteers in artillery practice.[6] When the expedition to Big Bethel was planned, he was detailed to accompany it along with two guns and ten men. He communicated that he believed the movement was poorly planned and would not be successful.[7]

When the Union army troops were repelled, he placed his guns in the middle of the road and fired to prevent pursuit by the enemy. He was advised by another officer to retreat, and he was quoted as saying, "I never dodge, and when the retreat is sounded I will leave and not before."[7] Just at the close of the action, when he had given the orders to withdraw his guns from the field, he was struck by a glancing cannon shot on the right temple and died almost instantly. For his bravery in the two days' action, he was brevetted captain, major, and lieutenant colonel, on the day of his death.[6]

Greble was the first Regular Army officer and United States Military Academy graduate killed in the American Civil War.[