70-pounder Whitworth naval gun

70-pounder Whitworth gun
Gun from Princess Royal, in Willard Park at the Washington Navy Yard
Type	Naval gun
Place of origin	United Kingdom
Service history
In service	1863–
Used by	Confederate States, United States, Brazil
Wars	American Civil War, Paraguayan War
Production history
Designer	Joseph Whitworth
Manufacturer	Joseph Whitworth
Unit cost	£3500
Produced	1863?–
Specifications
Weight	8,582 pounds (3,892.7 kg)
Length	118 inches (2.997 m)
Shell	Solid shot Explosive shell
Shell weight	81 pounds (36.7 kg)
Calibre	5.5-inch (140 mm)
Maximum firing range	5,540 yards (5,070 m)
Filling	Black powder
Filling weight	3 pounds 12 ounces (1.7 kg)

The 70-pounder Whitworth naval gun was designed by Joseph Whitworth during the 1860s. It was a rifled muzzle loader and used his hexagonal, rifled-bore design.

The Whitworth principle of rifling was thus described by the Report of the Armstrong & Whitworth Committee of the British War Office (1866):

[I]t may be described in general terms as a hexagonal bore with a rapid twist, although, strictly speaking, the bore is not hexagonal, but has 24 surfaces. The gun is, in the first instance, bored out cylindrically; a part of this original bore is left in the centre of each side of the hexagon, making six surfaces, then there are the coming out sides of the hexagon which give six more surfaces, and the going in sides giving also six surfaces, and lastly, the rounding off of the angles, which give six more, making 24 surfaces in all.

The projectile was hexagonal to match. The gun was highly accurate at long ranges, but the very precise manufacturing tolerances required a high standard of maintenance by the artillerymen. Wrote Jeff Kinard: "The odd shape of the projectile produced a weird, unnerving shriek as it traveled through the air."

Four guns were captured by the United States Navy on the blockade-runner Princess Royal on 29 January 1863. Two were sent to Morris Island, Charleston, South Carolina to bombard Fort Sumter during the summer of 1863. One gun had a premature detonation that killed four of its crew when trying to ram a projectile home. Another gun was disabled after 111 shots when its inner tube moved back far enough to block the vent.

A number of 70-pounders were bought by the Brazilian Navy and used to arm some of its ironclads during the Paraguayan War in the late 1860s. Teniente-coronel George Thompson (engineer) of the Paraguayan army recorded that the Brazilians cut the fuses to the wrong length, so the shells often failed to explode. Thousands of them were collected by the Paraguayans, who made a beautifully cast gun of their own at their foundry at Asunción – on the Whitworth principle – called the Criollo; this gun shot them back at the Brazilians.