He was assigned to the Washington Navy Yard in 1847. While there, Dahlgren established the U.S. Navy's Ordnance Department; became an ordnance expert; developed a percussion lock; and wrote a number of books, including "The System of Boat Armaments in the United States Navy", "Shells and Shell Guns", and "Naval Percussion Locks and Primers". Under his command, the Navy established its own foundry to manufacture new equipment, and its first product was the boat howitzer, designed for use aboard ship and in landings.