[1] This regiment was the outgrowth of a rifle battalion attached to the 1st brigade, 1st division of the Pennsylvania militia.

It crossed the Potomac on June 17, but the force soon returned to the Maryland side and encamped.

On July 2 the army moved to Martinsburg and thence after a fortnight, to Bunker Hill, Charlestown, and Harper's Ferry.

While in Martinsburg the 21st was presented with a beautiful flag by the loyal Union Germans of that city.

On August 9, the 21st boarded trains in Martinsburg, and returned to Philadelphia, via Harpers Ferry and Baltimore.