John Adolphus Bernard Dahlgren (November 13, 1809 – July 12, 1870) was a United States Navy officer who founded his service's Ordnance Department and launched significant advances in gunnery.

He then introduced a cast-iron muzzle-loading cannon with vastly increased range and accuracy, known as the Dahlgren gun, that became the U.S. Navy's standard armament.

In the Civil War, Dahlgren was made commander of the Washington Navy Yard, where he established the Bureau of Ordnance.

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.

While there, Dahlgren established the U.S. Navy's Ordnance Department; became an ordnance expert; developed a percussion lock; and wrote several books, including The System of Boat Armaments in the United States Navy, Shells and Shell Guns, and Naval Percussion Locks and Primers.

Dahlgren's meticulous research using gauges to measure pressure differences in the cannon barrel as it was fired resulted in a design that utilized slower-detonating gunpowder and merged characteristics of John Ericsson's experimental 12-inch "Orator" (and Robert Stockton's tragically executed imitation, the "Peacemaker") and the shell-guns adapted by French artillery officer Henri-Joseph Paixhans from their origination in the U.S. Army but named after him.

[1][3] Dahlgren wrote: Paixhans had so far satisfied naval men of the power of shell guns as to obtain their admission on shipboard; but by unduly developing the explosive element, he had sacrificed accuracy and range.

This made a mixed armament, was objectionable as such, and never was adopted to any extent in France ... My idea was, to have a gun that should generally throw shells far and accurately, with the capacity to fire solid shot when needed.

A bed-type carriage was used on small boats, with a rail system to allow the gun to be trained fore, aft, and broadside.

President Abraham Lincoln wanted to name then-Commander Dahlgren to the post of commander of the Washington Navy Yard.

The admiral was deeply troubled by Ulric's death and role in this event, as well as reports of the disrespectful treatment of the corpse before Richmond spymaster Elizabeth Van Lew secured its proper burial.

[5] However, despite Radical Republican associations, John Dahlgren's younger brother Charles G. Dahlgren (1811–1888), a banker and slave owner, became a Confederate brigadier general, commander of the 3rd Brigade, Army of Mississippi, which he personally recruited and funded, until his troops' integration into the regular Confederate army and removal by Jefferson Davis in 1862.