Civil War Union Army Officer. He began his Civil War service just days after the Confederate bombardment of Fort Sumter, South Carolina, being commissioned and mustered on April 27, 1861 as a 1st Lieutenant and Adjutant of the 4th New Jersey Militia regiment, a three-month enlistment unit raised hastily to meet the Confederate threat. He served with his unit as it first manned the defenses of Washington, DC, then as it took part in the July 1861 First Bull Run Campaign, where it was held in reserve. Mustered out on July 31, 1861 when his enlistment expired, he was subsequently commissioned as Major of the 4th New Jersey Volunteer Infantry (three-year enlistment) on August 17, 1861. A few days later he was moved up to Lieutenant Colonel of the regiment (September 7, 1861) when the officer originally commissioned to that position was recalled to Regular Army duty. He served as the 4th New Jersey's second-in-command through the Spring 1862 Peninsular Campaign, and took command of the regiment after the June 27, 1862 Battle of Gaines Mill, Virginia. In that engagement the 4th New Jersey's Colonel, James H. Simpson, and over 400 men were captured by Confederate forces. When he was exchange in late August 1862, Colonel Simpson was recalled to his Regular Army duties as a Major of Topographical Engineers, and William B. Hatch was promoted to full Colonel on August 26, 1862. He then led his regiment through its part in the triumphant charge of the 1st New Jersey Brigade at the September 15, 1862 Battle of South Mountain, and in the December 13, 1862 Battle of Fredericksburg. In that battle he led the 4th New Jersey as it charged and drove back men of a North Carolina regiment near a railroad embankment. While at the front of his troops his right leg was mangled by an exploding artillery shell. Carried to the rear, his leg was amputated, but the wounds proved grievous enough that he died two days later.