A first lieutenant when the Civil War erupted in 1861, Howard became colonel of the Third Maine, a volunteer regiment. In command of a brigade at Bull Run (Manassas) in July, he was promoted to brigadier general two months later. The next spring his right arm was badly shot up at Fair Oaks, and most of it had to be amputated. Howard returned to service in August 1862 and commanded troops at Antietam and Fredericksburg. Promoted to major general of volunteers in November 1862, Howard replaced Franz Sigel at the head of the XI Corps the next spring, much to the chagrin of many of its German-American troops. It was Howard's corps that Thomas "Stonewall" Jackson surprised and routed with his flank attack at Chancellorsville on 2 May 1863. Howard later claimed never to have received Union commander Hooker's warning of danger from the west. Whatever the case, both men had misread Robert E. Lee's daring division of his army, and neither adequately prepared the Union forces for an onslaught. Less than two months later Howard's men were again manhandled during the early stages of the battle of Gettysburg. Stampeded by Confederate forces north of town, they fell back to Cemetery Hill, where Howard, for a time the senior officer on the field, had left a unit in reserve and some artillery. The Confederates hesitated before the heights, allowing Winfield Scott Hancock, who took charge from a reluctant Howard, to construct the strong defensive line that sustained Union forces through the next two days.
Patrick G. Williams, "Howard, Oliver Otis," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-01243.html.