A resident of Chester County at the dawn of the American Civil War, Hampton S. Thomas became one of Pennsylvania's earliest responders to President Abraham Lincoln's call for volunteers to help defend Washington, D.C. following the mid-April 1861 fall of Fort Sumter to troops from the Confederate States Army.
Enrolling for military service on April 21 at the age of 23 in West Chester, Pennsylvania, Thomas then officially mustered in for duty the next day at Harrisburg as a third corporal with Company E of the 9th Pennsylvania Infantry.
Following the completion of his Three Months' Service, he was honorably discharged with his regiment on July 29.

 Two days later, Thomas re-enlisted.
Enrolling this time for a three-year term at Harrisburg on July 31, he mustered in at Camp Curtin on August 1, and was commissioned as a second lieutenant with Company G of the 1st Pennsylvania Cavalry that same day.
Transported to the Eastern theater of battle, he and his regiment were then attached to the U.S. Army of the Potomac.
On September 27, he was recommissioned as a first lieutenant.
Engaged with his regiment in skirmishing near Dranesville, Virginia on November 26, Thomas and his fellow 1st Cavalrymen received their first taste of combat while supporting a Union artillery battery during the Battle of Dranesville on December 20.
Assigned to scouting and defensive duties during the spring of 1862, they patrolled the areas around Catlett's Station, the Orange and Alexandria Railroad, Warrenton, and Rappahannock Station.
Appointed in April 1862 as assistant adjutant-general of the 1st Brigade under his former regimental commander, George Dashiell Bayard, who had been commissioned as Chief of Cavalry of III Corps (Union Army), Thomas and his men captured the town of Falmouth after chasing off the enemy during an early morning charge on April 18.
As a result of their success, Bayard was commissioned as brigadier-general of U.S. Volunteers on April 28, and Thomas was commissioned as a captain on May 5, and placed in charge of Company M. He and his men were then assigned to picket and scout details south of Fredericksburg, and advance guard and scouting details which supported the movements of Union Army commanding generals Irvin McDowell and George B. McClellan that spring and early summer.
Crossing the Shenandoah River, they then helped to cut off the movements of Confederate General Stonewall Jackson's men near Strasburg, and supported Pennsylvania's "Bucktails" in their fight against CSA troops near Harrisonburg on June 6 before moving on to Port Republic.
Standing in readiness, they next witnessed but did not engage in the Battle of Cross Keys (June 8).
Assigned again to picket and scout duties, their next combat engagements came in the Battle of Cedar Mountain (August 8), First Battle of Rappahannock Station (August 20–25), and the Second Battle of Bull Run (August 28–30).
Engaged next in the defense of Washington, D.C., Thomas and his men then resumed duties in support of McClellan's troops, engaging with the enemy in minor skirmishes and major charges throughout the fall.
During the Battle of Fredericksburg (December 11–15), they suffered heavily under intense fire from enemy artillery and infantry, losing a number of their current and former members, including Bayard who asked, after being mortally wounded, that David McMurtrie Gregg be placed in command of the brigade.

Appointed by Brigadier General Gregg as an inspector-general on the staff of the 1st Brigade on April 1, 1863, Thomas participated with the brigade in Stoneman's 1863 raid and then, that summer, led his 1st Pennsylvania Cavalrymen and two companies of the 1st Maryland Cavalry in the recapture of Union artillery at Fleetwood Hill during the Battle of Brandy Station, Virginia on June 9 as Union forces engaged those of Confederate General J.E.B. Stuart.
In a memoir penned in 1889, Thomas recalled what happened that day:
General Gregg was so unfortunate as to lose three guns of the Sixth New York Light Battery through the recklessness of Colonel Percy Wyndham, who comm
A resident of Chester County at the dawn of the American Civil War, Hampton S. Thomas became one of Pennsylvania's earliest responders to President Abraham Lincoln's call for volunteers to help defend Washington, D.C. following the mid-April 1861 fall of Fort Sumter to troops from the Confederate States Army. Enrolling for military service on April 21 at the age of 23 in West Chester, Pennsylvania, Thomas then officially mustered in for duty the next day at Harrisburg as a third corporal with Company E of the 9th Pennsylvania Infantry. Following the completion of his Three Months' Service, he was honorably discharged with his regiment on July 29.
 Two days later, Thomas re-enlisted. Enrolling this time for a three-year term at Harrisburg on July 31, he mustered in at Camp Curtin on August 1, and was commissioned as a second lieutenant with Company G of the 1st Pennsylvania Cavalry that same day. Transported to the Eastern theater of battle, he and his regiment were then attached to the U.S. Army of the Potomac. On September 27, he was recommissioned as a first lieutenant. Engaged with his regiment in skirmishing near Dranesville, Virginia on November 26, Thomas and his fellow 1st Cavalrymen received their first taste of combat while supporting a Union artillery battery during the Battle of Dranesville on December 20. Assigned to scouting and defensive duties during the spring of 1862, they patrolled the areas around Catlett's Station, the Orange and Alexandria Railroad, Warrenton, and Rappahannock Station. Appointed in April 1862 as assistant adjutant-general of the 1st Brigade under his former regimental commander, George Dashiell Bayard, who had been commissioned as Chief of Cavalry of III Corps (Union Army), Thomas and his men captured the town of Falmouth after chasing off the enemy during an early morning charge on April 18. As a result of their success, Bayard was commissioned as brigadier-general of U.S. Volunteers on April 28, and Thomas was commissioned as a captain on May 5, and placed in charge of Company M. He and his men were then assigned to picket and scout details south of Fredericksburg, and advance guard and scouting details which supported the movements of Union Army commanding generals Irvin McDowell and George B. McClellan that spring and early summer. Crossing the Shenandoah River, they then helped to cut off the movements of Confederate General Stonewall Jackson's men near Strasburg, and supported Pennsylvania's "Bucktails" in their fight against CSA troops near Harrisonburg on June 6 before moving on to Port Republic. Standing in readiness, they next witnessed but did not engage in the Battle of Cross Keys (June 8). Assigned again to picket and scout duties, their next combat engagements came in the Battle of Cedar Mountain (August 8), First Battle of Rappahannock Station (August 20–25), and the Second Battle of Bull Run (August 28–30). Engaged next in the defense of Washington, D.C., Thomas and his men then resumed duties in support of McClellan's troops, engaging with the enemy in minor skirmishes and major charges throughout the fall. During the Battle of Fredericksburg (December 11–15), they suffered heavily under intense fire from enemy artillery and infantry, losing a number of their current and former members, including Bayard who asked, after being mortally wounded, that David McMurtrie Gregg be placed in command of the brigade.
Appointed by Brigadier General Gregg as an inspector-general on the staff of the 1st Brigade on April 1, 1863, Thomas participated with the brigade in Stoneman's 1863 raid and then, that summer, led his 1st Pennsylvania Cavalrymen and two companies of the 1st Maryland Cavalry in the recapture of Union artillery at Fleetwood Hill during the Battle of Brandy Station, Virginia on June 9 as Union forces engaged those of Confederate General J.E.B. Stuart. In a memoir penned in 1889, Thomas recalled what happened that day:
General Gregg was so unfortunate as to lose three guns of the Sixth New York Light Battery through the recklessness of Colonel Percy Wyndham, who comm
Hampton S. Thomas