Perhaps the most unusual object of all the Civil War memorabilia found throughout the Navy Yard is the plaque on Building 28. The plaque states: "Within this wall is deposited the leg of Col. Ulric Dahlgren, USV, wounded July 6, 1863, while skirmishing in the streets of Hagerstown with the rebels after the Battle of Gettysburgh." On the day that Adm. John Dahlgren, inventor of the Dahlgren gun and then chief of the Bureau of Ordnance, was scheduled to lay the cornerstone of a new foundry at the Navy Yard, his son, Ulric, lay near death from a leg wound received in a fight with Rebel forces. It was decided that in order to save his life, the leg would have to be amputated. Admiral Dahlgren felt that a proper tribute to the bravery and courage exemplified by his young son would be a tablet on the corner of the foundry, where those who built the guns of war would be reminded that through the ages, men had always been willing to fight and sacrifice for what they believed was right.

The leg was brought to the Navy Yard in a flag-draped box and placed beneath the cornerstone of what is now the sheet metal shop, known as Building 28. Dahlgren recovered from the amputation but was killed while leading an attempt to free federal prisoners being held at Libby Prison in Richmond. When the original building was demolished to make way for a new one, the leg could not be found. Some say that Confederate sympathizers opened the wall and removed the leg; other people believe that it was removed and buried with Dahlgren's body after his death.

Stephen M. Forman, A Guide to Civil War Washington; Elliott and Clark, Washington DC, 1995, pp. 113-114.