The revolver of the Civil War was, of course, a percussion-cap weapon. Even with the powder and bullet contained in a combustible paper cartridge, loading such an arm was a slow process: each bullet had to be forced in the front of the chamber on top of its propellant charge by means of a hinged rammer under the barrel, and a tiny copper cap had to be placed on each nipple. It was nothing to attempt on a prancing horse. The Union cavalryman was armed with a single-shot carbine--the seven-shot Spencer repeater was not to make its battlefield appearance until late in 1863--and one revolver, giving him a total of seven shots without reloading. With a pair of six-shooters, Mosby had a five-shot advantage over any opponent he was likely to encounter. As he saw it, tactical strength lay in the number of shots which could be delivered without reloading, rather than in the number of men firing them. Once he reached a position of independent command, he was to adhere consistently to this principle. On July 14, 1862, General John Pope, who had taken over a newly created Union Army made up of the commands of McDowell, Banks and Fremont, issued a bombastic and tactless order to his new command, making invidious comparisons between the armies in the west and those in the east. He said, "I hear constantly of 'taking strong positions and holding them,' of 'lines of retreat,' and of 'bases of supplies.' Let us discard all such ideas. Let us study the probable lines of retreat of our opponents, and leave our own to take care of themselves." That intrigued Mosby. If General Pope wasn't going to take care of his own rear, somebody ought to do it for him, and who better than John Mosby? He went promptly to Stuart, pointing out Pope's disinterest in his own lines of supply and communication, and asked that he be given about twenty men and detailed to get into Pope's rear and see what sort of disturbance he could create. Stuart doubted the propriety of sending men into what was then Stonewall Jackson's territory, but he gave Mosby a letter to Jackson, recommending the bearer highly and outlining what he proposed doing, with the request that he be given some men to try it. With this letter, Mosby set out for Jackson's headquarters. He never reached his destination. On the way, he was taken prisoner by a raiding force of New York cavalry, and arrived, instead, at Old Capitol jail in Washington. Stuart requested his exchange at once, and Mosby spent only about ten days in Old Capitol, and then was sent down the Potomac on an exchange boat, along with a number of other prisoners of war, for Hampton Roads.