• Type: Rifled Gun, hexagonal rifling
• Rarity: Very Rare
• Years of Manufacture: 1861-1865
• Tube Composition: Steel
• Bore Diameter: 2.75 inches
• Standard Powder Charge: 1.75 lbs.
• Projectiles: 12 lb. hexagonal bolt
• Tube Length: 104 inches
• Tube Weight: 1,092 lbs.
• Effective Range (at 5°): 2600 yards
• Maximum Range (at 35°): 10,000 yards
• No. in North America: approx. 50 (US & CS)
• Invented By: Sir Joseph Whitworth
• Casting Foundry: Whitworth Ordnance Company, Manchester, England
• Special Notes: Although originally designed as a breechloader, muzzle-loading versions of this weapon were produced as well.

The 12-pounder Whitworth Breechloading Rifle, manufactured in England, was invented by Sir Joseph Whitworth, and imported into North America during the Civil War. It was a very rare gun during the war, but was an interesting precursor to modern artillery in that it was loaded from the breech and had exceptional accuracy over an enormous range. An engineering magazine wrote in 1864 that, "At 1600 yards the Whitworth gun fired 10 shots with a lateral deviation of only 5 inches." This degree of accuracy made them effective in counter-battery fire, used almost as the equivalent of a sharpshooter's rifle, and also for firing over bodies of water. They were not popular as anti-infantry weapons.

The 2.75 inch bore of the Whitworth was hexagonal in cross-section, and the projectile a long bolt that twisted to conform to the rifling. It is said that these bolts made a very eerie sound when fired, which could be distinguished from other projectiles.

Despite the great range and accuracy of this rifle, the Whitworth was difficult to keep operational. First, ammunition was unique to the rifle, and also expensive and difficult to import. Second, the breechloading mechanism was prone to jam, forcing many guns to be loaded as a conventional muzzle-loader of the era.

Although the Whitworths are of the generally associated with the C.S.A.--most were run through the Union blockade--there was one battery in Federal service in 1861. This battery only saw field service during the Peninsula Campaign in 1862, and for the remainder of the War was part of the defenses around Washington, DC.