The regiment was commanded by Colonel Samuel R. Curtis and spent several months guarding the Mexican border near Matamoras.

The 3rd Ohio was attached to Zachary Taylor's division in the Army of the Rio Grande commanded by General Winfield Scott.

[2] When the Civil War erupted, Samuel Beatty helped form a volunteer unit that mustered in as Company A of the 19th Ohio Infantry—the "Canton Light Guards."

[6] Beatty resumed command of his old brigade which was redesignated 1st Brigade of Van Cleve's 3rd Division, Major General Thomas Crittenden's XXI Army Corps, Army of the Cumberland, commanded by Major General George H. Thomas.

Beatty afterwards received the commendation of XXI Corps commander Thomas L. Crittenden, who wrote, "With pride I mention the name of Brig.

Instead, the junior officers of the Army of the Cumberland, confused by conflicting orders, continued their advance up Missionary Ridge.

The men of Wood's division and Beatty's brigade were among the first Federal soldiers to gain the crest of Missionary Ridge, and played a major role in routing the Confederate Army of Tennessee from their positions.

Beatty afterwards claimed to have captured eight pieces of artillery with limbers and caisson, 200 small arms, 176 prisoners and the commander and colors of the 42nd Alabama.

Beatty was elevated to command Wood's division, IV Corps, Army of the Cumberland prior to the Battle of Nashville.