See biography by his wife, Madeleine V. Dahlgren (1882).
Rear Admiral John Adolphus Bernard Dahlgren, USN, (November 13, 1809 – July 12, 1870), son of Bernhard Ulrik Dahlgren, merchant and 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 the war. For these achievements, Dahlgren became known as the "father of American naval ordnance."
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 muzzle loading cannon which came to bear his name (the Dahlgren gun) and be his most famous contribution.
His "Boat Howitzer" design was an improvement on the shell-gun invented by the French Admiral Henri-Joseph Paixhans. Dahlgren wrote:
The United States Navy had equipped several ships with 8-inch Paixhans guns of 63 and 55 cwt. in 1845, and later a 10-inch shell gun of 86 cwt. In 1854, the six Merrimack-class warships were equipped with 9-inch Dahlgren shell guns. By 1856, the Dahlgren gun 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 1864, well 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.
Admiral Dahlgren's son, Colonel Ulric Dahlgren, was killed during the Civil War in a cavalry raid on Richmond, Virginia, while carrying out an assassination plot against Jefferson Davis and the Confederate Cabinet. The plot is known as the Dahlgren Affair. The admiral was deeply troubled by his son's death and role in this event. Despite Radical Republican associations, John Dahlgren's younger brother Charles G. Dahlgren (1811-1888) was a strong proponent of slave ownership and was a Confederate Brigadier General, Commander of the 3rd Brigade, Army of Mississippi, which he personally funded.