At the end of the Revolution the navy practically ceased to exist, and Preble went into the merchant service, as so many of the officers were forced to do. But in 1798, when the quasi war with France took place, he re-entered the navy, which had been created anew. He was commissioned lieutenant in 1798, and was lucky enough the very next year to get the Essex, frigate of thirty-two guns. In her he started on what was then the longest cruise ever made by an American man-of-war. He went to the Indian Seas, to give convoy to a valuable fleet of merchant vessels engaged in the China and India trade, and which were liable to be attacked by French cruisers. He had no opportunity to distinguish himself especially in this duty, although he took care of the ships and got them all safely to New York. Soon afterward, the United States and France having come to terms, Preble went ashore and remained for two years. His health was bad in the beginning, but being much improved, in 1803 he reported for duty, and was assigned to the Constitution, forty-four guns, then preparing for a Mediterranean cruise. At that time the relations of the United States with the piratical powers of the Barbary coast were most unsatisfactory. After years of submission to their exactions,--a submission which seems almost incredible now,--the United States government determined to do in the end what it should have done in the beginning. This was to send a powerful squadron to attack these pirates of the land as well as the sea, and to force them to respect the persons and liberties of Americans. Preble was given the command of this squadron, with orders to punish Algiers, Morocco, Tunis, and especially Tripoli, so that it would not soon be forgotten. He hoisted the broad pennant of a commodore on the Constitution, and had under him the Philadelphia, a heavy frigate of thirty-eight guns, and five small vessels,--the Enterprise, Argus, Nautilus, Vixen, and Siren. It was a remarkable squadron in many ways. The Constitution was probably the heaviest frigate afloat, and able to withstand a cannonade as well as any line-of-battle ship. In Preble she had a commander worthy of her.