On May 24, 1861, Union troops crossed the Potomac River into northern Virginia and brushed aside a token defense at Arlington Heights and Alexandria. A few days later, on June 1st, a Union cavalry patrol was chased out of Fairfax Courthouse and a small skirmish erupted at Arlington Mills. Though minor, these incidents convinced Union war planners to proceed more cautiously. They would not advance deeper into this part of Virginia until mid-June.
Early in the morning on June 16th, Confederate Col. Maxcy Gregg of the 1st South Carolina Infantry Regiment left Fairfax Courthouse with 575 men from his regiment to conduct a reconnaissance toward the Potomac River. He linked up with a cavalry troop and Capt. Delaware Kemper with two 6-pdr guns from his Alexandria Light Artillery, then scouted the area. They made camp for the evening having observed only a few Union troops.
On June 17th, Union Brig. Gen. Irvin McDowell, commanding the Department of Northeastern Virginia, instructed Brig. Gen. Robert C. Schenck to send a regiment by rail to relieve the 69th New York Infantry Regiment, which had been guarding the Loudoun & Hampshire Railroad at Vienna. The Loudoun & Hampshire Railroad ran northwest from Alexandria to Leesburg and beyond.
Brig. Gen. Schenck took 697 men from the 1st Ohio Infantry Regiment and proceeded toward Vienna, leaving a few companies to guard points along the way. Companies E, C, G, and H, a total of 271 men, proceeded by rail, sitting on open platform cars.
Around the same time, Col. Gregg prepared an ambush along the railroad tracks near Vienna in case Union troops that had been observed in the area returned. Growing impatient, they formed up to march off, but just before 6pm they heard a train whistle in the distance. The ambush was re-laid.
As the train came around a curve, Kemper’s two cannon opened fire. Fortunately for the Ohio volunteers, they were able to jump from the open platform cars and dive into the woods and underbrush when the firing started, but not before eight were killed and four wounded. Companies G and H bore the brunt of the ambush. The train engineer panicked, detached his engine from the disabled cars, and made a hasty getaway toward Alexandria, leaving the Ohioans to fend for themselves.
The two sides exchanged fire, but the infantry was too far away to be effective.
Growing darkness ended the engagement, and the Confederates did not pursue even though they greatly outnumbered their foes. They did take one wounded soldier prisoner and returned to Fairfax Courthouse after midnight. The Ohioans returned to their camp on foot, using blankets to carry their remaining wounded. The next day, a local Unionist returned the dead to their regiment.
This was the last engagement in northeastern Virginia until the two main armies squared off along Bull Run in mid-July.
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