The smallest of the three principal classes of fighting ships were called sloops-of-war, or corvettes. These had sometimes two masts, sometimes three; but the particular feature that differentiated them was that they had but one row of guns in broadside, on an uncovered deck. The offices discharged by this class of vessel were various, but in the apprehension of the writer they may be considered rightly as being above all the protectors or destroyers of commerce in transit. All ships of war, of course, contributed to this end; but the direct preying upon commerce, upon merchant ships, whose resisting power was small, was done most economically by small vessels of relatively small power. Having a given amount of tonnage to devote to commerce destroying, many small vessels are more effective than a few big ones of unnecessary force. Such being the nature of the attack, the resistance must be similar in kind. That is, a flock of merchant ships being liable to attack by many small adversaries, several small protectors would be more efficient than one or two large ones. Sloops-of-war served also as despatch vessels and lookouts of a fleet, but were less well adapted to this service than the frigate was. THE FRIGATE AND HER GUNS This latter celebrated and favorite class of ship stood next in order of power above the corvette, with which it might also be said to have blended; for although in the frigate class there were two, or at the most three, rates that predominated vastly in numbers over all the rest, yet the name covered many differing degrees of force. The distinguishing feature of the frigate was that it carried one complete row of guns upon a covered deck—upon a deck, that is, which had another deck over it. On this upper or spar deck there were also guns—more or fewer—but lighter in weight than those on the covered deck, usually styled the main deck. The two principal classes of frigates at the beginning of this century were the thirty-two-gun and the thirty-eight-gun. That is, they carried nominally sixteen or nineteen guns on each side; but the enumeration is misleading, except as a matter of comparison, for guns of some classes were not counted. Ships generally had a few more cannon than their rate implied. The United States thirty-two-gun frigate _Essex_, for example, carried at first twenty-six long twelves on the main deck, with sixteen carronades and two chase guns on the spar deck. Above these two classes came the forty-four-gun frigate, a very powerful rate, which was favored by the United States navy and received a development of strength then unprecedented.