In response to the need for a lighter weapon than the Walker Colt and the Patterson Colt, Samuel Colt designed a lighter revolver called the Pocket Model, a revolver of .31 caliber. Need for a larger caliber resulted in the Colt 1851 Navy, the most popular handgun of the early (pre-Civil War) American West. The 1851 Navy was a .36 caliber, 6-shot revolver that weighed 2 lbs 4.5 oz, half the weight of the Walker. This revolver, like its predecessors, used a percussion cap for ignition, and each cylinder would be individually loaded with black powder and ball, by use of a built in loading lever. Colt Navy revolvers were not necessarily related to sales to the Navy, but were a favorite revolver in the Crimea War among Brits, and the Civil War for both North and South. Colt Navy Revolvers were the favorite sidearms of dozens of figures in the American West, including Pony Express riders, Doc Holliday, John
Singleton Mosby, Wild Bill Hickock and Buffalo Bill Cody. The Pony Express riders carried a Colt Navy and one or two spare loaded cylinders for emergencies.
More about the Colt Navy Revolver by someone who REALLY knows what he's talking about, at Texas Ranger Magazine. The patent below is the right basic configuration and date for the Colt Navy, but the Colt Navy had a longer barrel.