Joseph K . Mansfield Joseph King Fenno Mansfield ( December 22 , 1803 – September 18 , 1862 ) was a career United States Army officer , civil engineer , and a Union general in the American Civil War , mortally wounded at the Battle of Antietam . Early life . Mansfield was born to Henry and Mary Fenno Mansfield in New Haven , Connecticut , a cousin of Joseph G . Totten . He entered the United States Military Academy when he was fourteen and graduated second in a class of forty in 1822 . He then became a resident of Middletown , Connecticut before and during his military career . He was commissioned a second lieutenant in the U . S . Army Corps of Engineers . Advancement came slowly in the peacetime Army and he was promoted to first lieutenant in 1832 , captain in 1838 . In the Mexican - American War , he received a brevet promotion to major for the action at Fort Brown , Texas , on May 9 , 1846 . He was wounded in the leg at the Battle of Monterrey , and he received a brevet promotion to lieutenant colonel for his actions there . He was appointed a brevet colonel for the Battle of Buena Vista in 1847 . After the war he was promoted to colonel and Inspector General of the U . S . Army on May 28 , 1853 . Civil War . At the start of the Civil War , Mansfield commanded the Department of Washington ( April 27 - August 17 , 1861 ) , and was promoted to brigadier general on May 6 , 1861 . He was stationed at Hatteras Inlet , North Carolina , in October , following the battle fought there by Benjamin Butler in August . He was a brigade commander in the Department of Virginia from March to June 1862 . His only combat activity during this period was the firing of coastal batteries from Hampton Roads against the ironclad " CSS Virginia " in its naval battle against the " USS Monitor " on March 9 , 1862 . Until the fall of 1862 , Mansfield commanded the Suffolk Division of the VII Corps of the Department of Virginia in the vicinity of Suffolk . During the Maryland Campaign , when Confederate General Robert E . Lee invaded the North for the first time , Mansfield was given command of the XII Corps of the Army of the Potomac , as of September 15 , 1862 , two days prior to the Battle of Antietam . He arrived in the camp with 40 years of army experience , but no recent combat . He was white - haired and white - bearded , but had a vigorous manner that belied his age . His officers considered him nervous and fussy , but his men , many of whom were new recruits , liked him well enough due to his shows of blustery enthusiasm and fatherly assurance . On the morning of September 17 , 1862 , the I Corps under Maj . Gen . Joseph Hooker attacked from the north , parallel to the Hagerstown Turnpike , smashing into the Confederate left flank . Mansfield ' s corps came immediately behind . As the lead brigade moved through an open field east of the Miller farmstead , they were subjected to fire by Confederate gunners , who took a terrible toll on the rookie soldiers . The troops were advancing in column formation , more suitable for marching , and their officers ordered deployment into open battle lines , which would reduce the risk of casualties from artillery shelling . Mansfield countermanded these orders , insisting they stay in column , because he was concerned that outside of the immediate control of their officers , the men would break and run . The result of this was to improve the mass of men that descended on the Confederate lines . Mansfield personally led troops on his left flank , from the brigade of Brig . Gen . Samuel W . Crawford , in the East Woods . He returned to the rear to bring up more troops , and when he reached the line again he saw soldiers from the 10th Maine Infantry regiment firing into the woods . Mansfield , assuming that men from Hooker ' s corps were in the woods , rode down the regimental line crying out , " You are firing on our own men ! " The soldiers convinced Mansfield that in fact they were not and were receiving heavy fire from the woods . Mansfield replied , " Yes , yes , you are right , " and just then his horse was hit and a bullet caught him squarely in the right chest . Writes Dr . Patrick Henry Flood , Surgeon , 107th NY Regiment , in a letter to his widow , " I found the clothing around his chest saturated with blood , and upon opening them , found he was wounded in the right breast , the ball penetrating about two inches from the nipple , and passing out the back , near the edge of the shoulder blade . " He was taken to a field hospital at the George Line farm in Sharpsburg , where he died the next morning . He is buried in Indian Hill Cemetery , Middletown , Connecticut , and received a posthumous promotion to major general , backdated from July 18 , 1862 , for his gallantry at Antietam . Alpheus Williams became acting commander of XII Corps after Mansfield fell . Fort Mansfield , a coastal artillery installation in Westerly , Rhode Island , was named in his honor . Mansfield Avenue in the Antietam National Battlefield was also named for him . The Middletown Mansfields baseball team was named for him as well . His nephew , Lt . Howard Mather Burnham of the 5th U . S . Light Artillery , Battery H , was killed in action in 1863 at the Battle of Chickamauga .