He transferred to the infantry early in the war and led a brigade at Cedar Mountain which routed a division that included Stonewall Jackson’s unit, though it was later driven back.

He was severely wounded at Antietam and returned to action at Gettysburg, where his division drove the Confederates out of "the valley of Death" beside Little Round Top, with Crawford dramatically seizing the colors and leading from the front.

[3] Crawford was the surgeon on duty at Fort Sumter, South Carolina, during the Confederate bombardment in 1861, which represented the start of the Civil War.

[4] A month after Fort Sumter, Crawford decided on a fundamental career change and accepted a commission as a major in the 13th U.S. Infantry.

The wound took eight months to heal properly and he was unable to return to the field until May 1863, when he was given command of the Pennsylvania Reserves Division in the defenses of Washington, D.C.

In commanding this division, Crawford was following in the footsteps of two Union Army luminaries: John F. Reynolds and George G. Meade.

Furthermore, the troops of his division had just spent six months on easy garrison duty around Washington and were not fully combat ready.

He was ordered to the front to assist the brigade of Col. Strong Vincent on Little Round Top, but the battle had already petered out by the time his division arrived.

Meanwhile, the Confederate troops of Lt. Gen. James Longstreet's Corps had swept through the Devil's Den, driving the Union defenders back to Plum Run, a stream just to the west of Little Round Top, and an area that became known to the soldiers as "the Valley of Death".

Crawford's division swept down the slope of Little Round Top along with the brigades of Colonels William McCandless and David J. Nevin.