In 1785, Barbary pirates, most notably from Algiers, began to seize American merchant vessels in the Mediterranean. In 1793 alone, eleven American ships were captured, and their crews and stores held for ransom. To combat this problem, proposals were made for warships to protect American shipping, resulting in the Naval Act of 1794.[8][9] The act provided funds to construct six frigates, but included a clause that if peace terms were agreed to with Algiers, the construction of the ships would be halted.[10]
Joshua Humphreys' design was unusual for the time, involving a diagonal scantling (rib) scheme intended to restrict hogging while giving the ships extremely heavy planking. This design gave the hull a greater strength than a more lightly built frigate. Humphreys' design was based on his realization that the fledgling United States of the period could not match the European states in the size of their navies. This being so, the frigates were designed to overpower other frigates with the ability to escape from a ship of the line.[11][12][13] However, the Congress was a scaled-down version of his more famous designs for the Constitution, United States and President, being closer in size to the standard European frigates of the day, and mounting the usual armament of 18-pounder guns