With the outbreak of hostilities, Pleasants became a
second lieutenant in the 6th Pennsylvania Volunteer Infantry, which enlisted for only three months. He re-enlisted as a
captain in the
48th Pennsylvania Volunteer Infantry Regiment in July 1861. The regiment initially saw service in the
Western Theater but came to the
Eastern Theater and fought in such battles as
Antietam,
Second Bull Run,
Fredericksburg and in
the Wilderness. By 1864, Pleasants had risen to
lieutenant colonel and commanded the 48th Pennsylvania, which was one of the units outside Petersburg. Many of the 48th were coal miners, and Pleasants supposedly heard his men suggest running a shaft under the Confederate lines. Pleasants went to his superiors, who approved the plan. He battled a lack of supplies as well as a lack of interest on the part of Union generals until other attacks on Petersburg had failed. He was successful in his construction to such an extent that the explosion killed nearly 300 Confederate soldiers. However, the Union troops, under
Ambrose Burnside, failed to take advantage of the explosion and suffered considerable casualties in what is known as the
Battle of the Crater. The Confederates recovered their original position. Pleasants was appointed to temporary command the 2nd Brigade, 2nd Division,
IX Corps, June 18, 1864, to June 25, 1865. His brevet appointment citation specifically mentions his service at Petersburg. ==Later life==