John Adolphus Bernard Dahlgren (November 13, 1809 – July 12, 1870) was a United States Navy leader. He headed the Union Navy's ordnance department during the American Civil War and designed several different kinds of guns and cannons that were considered part of the reason the Union won the war. For these achievements, Dahlgren became known as the "father of American naval ordnance." He reached the rank of rear admiral.