Rear Admiral John Adolph Dahlgren, USN, (1809-1870), son of the Swedish Consul in Philadelphia, Pennsylvania, made his career in the United States Navy. 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 that war.

The young John Dahlgren joined the United States Navy in 1826 as a midshipman and was promoted to the coastal survey in 1834. By 1847 he was an ordnance officer, and at the Washington Navy Yard began to improve and systematize the procurement and supply system for weapons.

Under his command, the Navy established its own foundry, and its first product was the Boat Howitzer which was designed to be used on both ship and in landings. But it is his cast iron cannon, which came to bear his name (the Dahlgren gun), which was his most famous contribution. By 1856, it had become the standard armament of the United States Navy. However, fatefully, one of the "dahlgrens" exploded on being tested in 1860, causing navy regulations to require the use of much lower levels of powder until into the civil war. The commander of USS Monitor felt that had his gunner packed the cannons with a full charge, he might have been able to destroy CSS Virginia.

Dahlgren himself took charge of the Washington Navy Yard in 1861, and in 1863 took command of the South Atlantic Blockading Squadron. In 1864 he helped William Tecumseh Sherman secure Savannah, Georgia. In 1869, he returned to the Washington Navy Yard where he served until his death.

The Naval station in Dahlgren, Virginia, and Dahlgren Hall at the U.S. Naval Academy in Annapolis, Maryland, were named for him, and so was Dahlgren, Illinois.

See also: John Ericsson