Even though the USS Monitor was proclaimed the “little ship that saved the Union,” this experimental ironclad had numerous design flaws. The Monitor’s inventor, John Ericsson, set about to improve the design which resulted in the Passaic-class of monitor ships. Ericsson added XV-inch Dahlgren guns to compliment the XI-inch shell guns in each turret, improved the protecting armor, and enhanced the hull design, making this class of monitors more seaworthy. In all, 10 were constructed, and they all served well during the war. Two were sunk off Charleston, South Carolina: the USS Weehawken, overtaken by a swell that flooded its hatches, and the USS Patapsco, hit by a torpedo. The Passaic-class proved to be the ironclad backbone of the Union’s blockading squadrons during 1863.