Civil War Union Major General. He commanded the IV Corps of the Union Army of the Potomac during the first half of the American Civil War. The son of a renowned physician and surgeon, he moved with his family to Kennebec County, Maine as a youth. He decided to pursue a military career and enrolled in the US Military Academy at West Point, New York, graduating 10th out of a class of 45 in 1832, and was commissioned a brevet second lieutenant in the 3rd US Artillery. He served in Charleston Harbor during the nullification crisis of 1832 to 1833, and served as an aide to General Winfield Scott from 1837 to 1841. After being promoted to the rank of captain in November 1841, he served in various garrisons until 1844 and then functioned as an artillery and cavalry instructor at US Military Academy. In 1854 he was sent with the US 3rd Artillery Regiment around Cape Horn to California and served on the Pacific frontier in garrison duty and Native American campaigns in the Northwest. Promoted to the rank of major in October 1858, he returned to Washington DC near the end of 1859 and became General Winfield Scott's military secretary from January until April 1861. In May 1861, after the outbreak of the Civil War, he was promoted to the rank of colonel of the 11th U.S. Infantry, serving briefly on the staff of New York Governor Edwin D. Morgan until June 25, 1861, overseeing that state's raising of militia. On July 21, 1861, at the First Battle of Bull Run, he commanded the 1st Brigade, 1st Division (Tyler), and then led Keyes's Brigade, before assuming command of a division from November 1861 until March 13, 1862. In August 1861 he was promoted to the rank of brigadier general of volunteers with date of rank of May 17, 1861, the third-ranking brigadier general in the Army. He was then given command of IV Corps, leading it from its inception on March 3, 1862, until its discontinuation on August 1, 1863. He saw action at Lee's Mill, Yorktown, Bottom's Bridge, Savage's Station, Seven Pines (Fair Oaks), Charles City Cross Roads, Malvern Hill, and Harrison's Landing. For gallantry at Fair Oaks, Keyes received the brevet of brigadier general in the regular army. On March 12, 1863, President Abraham Lincoln nominated Keyes for promotion to the grade of major general, U.S. Volunteers, to rank from May 5, 1862 and the US Senate confirmed the award on March 13, 1862. In addition to the IV Corps, he commanded the Yorktown District, VII Corps, and the division at Suffolk. Among Keyes's other military actions were the raid to White House, Virginia, on January 7, 1863, and the expedition to West Point, Virginia, on May 7, 1863. During the Gettysburg Campaign in July 1863, he fell afoul of General John Adams Dix's strategic plan to demonstrate heavily against Richmond in order to divert Confederate reinforcements from General Robert E. Lee's army in Pennsylvania. He retreated from a position near what is now Tallysville, Virginia, in the face of what Dix deemed to be inferior forces, so Dix had Keyes removed from command. He requested an investigation of the charges that led to his removal but it was never granted. He then served on various boards and commissions, including the board for retiring disabled officers from July 1863, until his resignation and retirement from the US Army in May 1864, with 32 years of continued military service. Following his retirement, he moved to San Francisco, California where he became financially successful and prominent. He was president of a Mexican gold mining company from 1867 to 1869, and vice president of the California vine-culture society from 1868 to 1872. He also was engaged in the savings and loan business. He was the author of "The Rear Guard at Malvern Hill" as part of The Century Company's "Battles and Leaders of the Civil War" series, as well as "Fifty Years' Observation of Men and Events" (1884), later reprinted as "Fighting Indians in Washington Territory" (1988). His work "From West Point to California" was published posthumously in 1950. While on a trip to Europe with his wife, he died in Nice, France, at age of 85.