The Whitworth Rifle, named after its creator Joseph Whitworth (1803-1887) of England, was a rifled field gun seeing service during the American Civil War (1861-1865). The type did not enjoy the numbers nor exposure of its competing brethren but was notable in that it was an artillery piece loaded from the breech (rear) of the gun tube at a time when artillery was still generally loaded from the muzzle (as in the Napoleon 12-pounders popular with both the Federals and Confederates). Whitworth Rifle production took place overseas in Britain which made its availability in the States rather restricted.
The Whitworth Rifle was regarded as an excellent field piece of particular accuracy at range - especially for counter-battery fire where the weapon could hit massed, stationary targets out to 1,600 yards (4,800 feet) with some regularity (some sources state accuracy out to 10,000 yards!). The base design was given a 2.75 inch (12-pounder) gun tube with a hexagonal bore and this sat atop traditional mounting hardware involving a tow arm and a pair of multi-spoked road wheels. Like other artillery pieces of the period, the Whitworth Rifle was towed into and out of action by beasts-of-burden though its wheels could allow a gunnery crew to relocate / retrain the gun over short distances. Another version was made in 2.17" (6-pounder) caliber.
The Rifle fired a nearly-13-pound, flat-sided projectile which was spirally-grooved so as to better adhere to the gun tube's rifling (making the projectile quite accurate over range as a result). The spiraling concept was patented before the Civil War in 1855. Whitworth attempted to interest the British Army in his field piece but was rebuffed so some of his guns ended up in the United States in Confederate hands (some were captured by Union forces).
One of the major drawbacks in the Whitworth Rifle's design was the breech system's fragility over the course of extended combat exposure. This led crews to eventually permanently seal the breech action and load/reload their guns from the muzzle in the typical fashion - negating the weapon's one true distinct quality.
Whitworth also designed an infantry service rifle known plainly as the "Whitworth Rifle" to succeed the Enfield Pattern 1853 guns of .577 caliber. This rifle, like the Whitworth Rifle field gun, also made use of a hexagonal bore (0.451 caliber) firing an elongated hexagonal bullet. Again, the British Army passed on this local design but the long gun was adopted by both the French Army and the Confederate States of America.