John Adolphus Bernard Dahlgren (1809-1870), US admiral, standing by a Dahlgren gun on the desk of the USS Pawnee. Dahlgren served in the US Navy during the US Civil War (1861-1865), rising to the rank of Rear Admiral. He designed several guns and cannons that helped the Union forces defeat the Confederacy. The Dahlgren gun seen here was an improved cannon that was thicker at the breech end (right) than the muzzle (left). Further advances in artillery technology soon rendered this design obsolete. Photographed on 17 June 1865, in Charleston Harbor, South Carolina, USA. This photograph is from the collection of the US Civil War photographer Mathew Brady.