Dam Number 4

The Confederates attempted to damage Dam Number 4 on the Chesapeake and Ohio Canal in June and December 1861.

Dam Number 4, located fifteen miles below Williamsport, was the fourth of seven dams built in the Potomac River to impound and divert water from the river into the Chesapeake and Ohio Canal. Construction of the dam commenced September 1832 and was completed in June 1835. The dam was initially built of cribs, which were hollow cages built of heavy timbers that were anchored to the riverbed, filled with rock and sheeted with planks. A series of floods in 1857 seriously damaged Dam Number 4. Temporary repairs were made and in 1861, a contractor replaced the crib dam with a masonry structure.

Before evacuating Harpers Ferry, Confederate Gen. Joseph E. Johnston sent work parties to the Potomac to breech Dam Number 4, hoping to disable the canal prior to his evacuation of Harpers Ferry. On June 10, 1861, the Confederates made their first attempt, but were unable to harm the new masonry structure. On June 13 the Confederates were observed drilling holes in the solid rock abutment of the dam for a black powder charge, but they were driven away by the Sharpsburg Rifles and another company from Boonsboro.

On December 11 Confederate Gen. Thomas J. “Stonewall” Jackson sent a small force, led by Turner Ashby, to disable Dam Number 4. In the mid-morning the Confederates fired artillery rounds at the Twelfth Indiana Volunteers who protected the dam on the Maryland side. A raiding party with boats approached the river opposite the guard lock about a mile above the dam, while another party approached the river at a gristmill below the dam. Heavy infantry fire from the Union side compelled Ashby to withdrawn his men. Later a small number of Indiana soldiers crossed to Virginia to determine if the Confederates had left and were taken prisoner. No damage was done to the dam.