On July 7, 1863 they joined their Division at Frederick, Md., and began the pursuit of General Lee on July 7-24. The regiment engaged in their first battle at Wapping Heights July 23. The Bristoe Campaign began October 9 through October 22.  Next the Regiment advanced to the line of the Rappahannock November 7-8. They were also involved in Kelly's Ford on November 7 and Brandy Station November 8. Hezekiah O'Neal was accidentally wounded November 12 and died December 4, 1863 in Lincoln Hospital in Washington, D.C. He is buried at East View Cemetery, in Chaneysville, PA.

The Mine Run Campaign bwgan on November 26 until December 2, 1863. The Battle of Payne's Farm was November 27. The Regiments next engagemant was the Demonstration on the Rapidan February 6-7, 1864. Next was the Dirty and then they were near Brandy Station until May. The Rapidan Campaign lasted from May 4 to June 12. The Battle of the Wilderness took place May 5-7; On May 6 Jonathan Snider received his first wounds as a soldier.

The Regiment was at Spottsylvania May 8-12 and the Spottsylvania Court House Engagement began on May 12-21. On May 12, John Ellsworth O'Neal was slightly wounded. From a submission to the Pioneer Library in Bedford County, Pa; by Dorothy O'Neal Grim on September 28, 1987 we learn the following: This account appeared in the COMPENDIUM OF BIOGRAPHY,  by Olgie, 1896,, Miner County, South Dakota: J.E. O'Neal, a progressive and up-to-date farmer of Miner County, whose home is in section 30, Clinton Township, is a native of Bedford county, Pennsylvania, born February 5th, 1843,, a son of William and Ary (Robinson) O'Neal, the former a native of Pennsylvania and the latter a native of Vermont. The parents lived and died in Bedford county, Pennsylvania.

Mr. O'Neal was reared on a farm in Bedford County and educated in the district schools there. August 17, 1862 he enlisted in Company D, One
Hundred and Thirty-eighth Pennsylvania Volunteer Infantry and was first sent to Relay House near Baltimore. In June (1863) he went to Harper's Ferry and joined the Army of the Potomac, under General Mead and took part in the following engagements: Snicker's Gap, Grande Station, Cedar Grove, Mine Run, Brisker Station, Cedar Mountain, Rappahannock Station, battle of the Wilderness under Grant, Spottsylvania, North Anna, Cold Harbor, the Siege of Petersburg and tearing up of the railroad at Reems Station. Pearl O'Neal said that at St. Petersburg, Va. Near Richmond, Grandpa O'Neal tunneled under the Confederate lines because they couldn't break through the confederate lines. The opening to the tunnel is still there. Union Soldiers blew up lines. Confederate reorganized and it didn't accomplish the purpose.

John O'Neal lied about his age to get into the Army. The Army was then sent to the Shenandoah Valley by the way of Baltimore, from there to Battle of Monocacy Junction and to Washington, District of Columbia. He then participated in Sheridan's Raid in the Shenandoah Valley, the battle of
Opagan Creek, Winchester, Fisher Hill, Harrisburg, Cedar Creek and then returned to Petersburg and spent the winter in Fort Ducham. The following year came to Siege of Richmond, Appomattox and the surrender of Lee's Army; after which our subject marched with the command to Columbia and participated in the Grand Review and then encamped at Washington until June 23, 1865. During the war Mr. O'Neal received several slight wounds, but never missed a battle in which his regiment participated.

The Assault on the Salient was conducted on May 12 1864. On May 23-26 the North Anna River Battle occurred. More on the North Anna River Battle. Next came the the  line of the Pamunkey May 26-28, followed by the Totopotomoy May 28-31.

The Cold Harbor Battle was 12 days long, from June 1-12. John Nycum was wounded and died at Cold Harbor, VA June 28, 1864; and is buried at Arlington National Cemetery.More on the Cold Harbor Battle. After this battle the 138th began marchibg towards Petersburg June 17-18. Their next skirmish was held on  Jerusalem Plank Road, Weldon Railroad, June 22-23. Following that, they were involved in the Siege of Petersburg until July 6.

After the siege the, 138th marched to Baltimore, Md., on July  6-8. to engage the confederates in the Battle of Monocacy on July 9. David Snider was wounded at this battle on July 9, 1864.  Then again, they were off in Pursuit of Early to Snicker's Gap on July 14-24.

Next came Sheridan's Shenandoah Valley Campaign which lasted from August to December of 1864. The 138th was in Charlestown on August 21-22.
Then on to the Battle of Opequan, Winchester, September 19, followed by Fisher's Hill, September 22 and then the Battle of Cedar Creek, October 19. At the Battle of Cedar Creek, Johnathon Snider was wounded again, this time fatally, and he died October 22, 1964.

Next came the Appomattox Campaign More on Appomattox. March 28-April 9 and the assault on and fall of Petersburg April 2. The Battle of Appomattox Court House  took place on April 9, 1865 and resulted in the surrender of Lee and his army.

The 138th marched to Danville April 23-27, and pulled duty there until May 23. From there they marched to Richmond, Va., then to Washington, D. C., May 23-June 3. The Corps Review took place on June 8 and the 138th Regiment of the Pennsylvania Volunteer Infantry was Mustered out June 23, 1865.

 The 138th Regiment lost during service 6 Officers and 90 Enlisted men killed and mortally wounded. 1 Officer and 70 Enlisted men by disease, for a total loss of 167 of Pennsylvania's Finest.