John A. Dahlgren, American admiral (d. 1870)
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.

Dahlgren devised a smoothbore howitzer, adaptable for many sizes of craft and shore installations. 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. In 1863, he took command of the South Atlantic Blockading Squadron at the rank of rear admiral. He helped William Tecumseh Sherman secure Savannah, Georgia.