The 3-pdr rifle was designed by British manufacturer Joseph Whitworth in the early 1850s. Along with Whitworth's 12-pdr rifle, the artillery piece was considered for adoption by the British government's Board of Ordnance, eventually losing out to the Armstrong gun.^[1] During the American Civil War the weapon was imported and saw service in the Union army and possibly^[2] in the Confederate army. In service, the rifle was sometimes referred to as a mountain gun, though this might stem from a confusion over caliber sizes.^[3]

From a design standpoint, the weapon was unique. Like all of Whitworth's designs, the weapon had a hexagon-ally rifled barrel. It was also a breechloader, an unusual feature for the time. The piece had exceptional range and accuracy, being capable of firing a 3-pound shell over 9,500 yards.^[4] However, the small size of the shell limited its bursting charge, consequently reducing the number of fragments formed when the shell detonated.^[4] According to a 1860 New York Times article covering Whitworth's weapons, the relatively small 3-pdr had superior range compared to his larger rifled guns.^[5]