Speed is the sloop’s weapon: a ketch-rigged sloop is capable of sailing very close to the wind, far closer indeed than many larger ships. This ability allows it to stay out of trouble, most of the time, if under a competent master. This is fortunate, as a sloop does not have the weight of shot, being armed with relatively light six-pounder cannon; or structural strength to last very long against a real battleship.
A sloop was hardly ever the command of a post-captain, a man who was on the permanent list of naval officers. The commanding officer of a sloop was called “captain”, at least to his face, but his official title was usually “master and commander”; his rank, and pay, was that of lowly lieutenant. Commander as a naval rank, as opposed to job title, was a later development. This is why, somewhat confusingly to civilians, a naval commander is outranked by a naval captain, and it is still something that baffles Hollywood scriptwriters from time to time. Command of a sloop, however, was a chance for a young officer to get away from stuffy superiors and to shine in his own right as an aggressive and successful leader.