On June 8, U.S. Gen.-in-Chief Winfield Scott ordered Col. Charles P. Stone, 14th U.S. Infantry, to lead a column of volunteers northwestward from Washington, D.C. Stone was instructed to cover the upper Potomac against Confederate incursions, to staunchthe flow of Confederate supplies from Baltimore to Virginia, to open the obstructed Chesapeake & Ohio Canal near Leesburg, Virginia, and to "give countenance to our friends in Maryland." If possible, he was also to link up with the army of Maj. Gen. Robert Patterson, about to leave Pennsylvania for operations in western Virginia near Harper's Ferry.
Stone started from the capital's suburbs 2 days later, marching up the Maryland side of the Potomac with 2,500 troops of all arms-- 3 regiments and 4 battalions of infantry, 2 mounted companies, and 2 cannon. The movement proceeded smoothly to Tennallytown and Rockville, Maryland, which his troops occupied on the 11th, sending waves of alarm through Confederate enclaves as far west as Harper's Ferry. From Rockville, where Stone established his headquarters, detachments fanned out to numerous towns along the river, including Seneca Mills (where they skirmished with local Confederates on the 14th), Great Falls, and Darnestown. By these movements, the Federals secured the C & O Canal almost as far north as Edwards' Ferry and protected the property of numerous Unionists. On the 15th, the expedition reached Edwards and Conrad's ferries, the main approaches to strategic Leesburg.
The next day, Stone found Confederate forces of undetermined size moving against him from Leesburg, and on the 17th, a skirmish, primarily a long-range artillery duel, broke out in that sector. When some of the Confederates attempted to cross at Edwards' ferry, Stone's cannon fire blasted them into retreat. Hesitating to occupy Leesburg against unknown opposition, he marked time at Poolesville, between Edwards' and Conrad's ferries, till on the 30th, when Scott ordered him to join Patterson near Martinsburg, Virginia, northwest of Harpers ferry.
Leaving a rear guard to secure the canal and the ferries for as long as possible, the colonelmoved upriver. On July 4th, Stone crossed the Potomac at Harpers Ferry, where he had a long-range clash with the rear guard of Gen. Joseph E. Johnston's army, which had recently evacuated the town. Reaching Martinsburg on the 7th, he assumed command of a brigade in Patterson's army. Though Stone's expedition was of only moderate strategic significance, Gen. Scott reported himself "highly pleased" by its conduct.