[ Autographs ] John A. Dahlgren 1809-1870 Union rear admiral inventor of the cannon which bore his name, also commanded the South Atlantic Blockading Squadron. Fine scientific content A.D.S. 1p. 4to. Washington Navy Yard, July 27, 1847 wherein Dahlgren writes a memorandum concerning an important ordnance improvement, his "Trial of a Perforated Hammer head" for an eight-inch gun and lists eight trial firings, including one which resulted in the gun's recoil tearing off a securing cleat. He concludes: "..The Hammerhead was not moved by the reaction of any of the above firings... Every charge was fired when the primer exploded. And every primer of 50 was exploded, save one...' Two years later, Dahlgren presented the Navy with his plans for his new land-and-sea cannons, later called "Dahlgren guns". Fine condition.