Dahlgren, John A., American naval officer, was born at Philadelphia in 1809, and at a comparatively early age turned his attention to the construction of heavy guns. In 1847 he became chief of the Ordnance Department at Washington, and while there invented the smooth-bore guns which bear his name. In 1863 he was given command, as rear-admiral, of the South Atlantic squadron, with which he organised the blockade of Charleston, and made several fierce attacks on the seaward defences of the town. These culminated in a gallant but unsuccessful assault on Fort Sumter. The admiral died in 1870.