Union efforts to retake Charleston Harbor began on April 7, 1863, when Rear Admiral Samuel Francis Du Pont, commander of the South Atlantic Blockading Squadron, led the ironclad frigate "New Ironsides", the tower ironclad "Keokuk", and the monitors "Weehawken", "Passaic", "Montauk", "Patapsco", "Nantucket", "Catskill", and "Nahant" in an attack on the harbor's defenses. (The 1863 Battle of Fort Sumter was the largest deployment of monitors in action up to that time.) The attack was unsuccessful: the Union's best ship, USS "New Ironsides" never effectively engaged, and the ironclads fired only 154 rounds, while receiving 2,209 from the Confederate defenders . Due to damage received in the attack, the USS "Keokuk" sank the next day, off the southern tip of Morris Island. Over the next month, working at night to avoid the attention of the Federal squadron, the Confederates salvaged "Keokuk's" two eleven-inch Dahlgren guns . One of the Dahlgren guns was promptly placed in Fort Sumter.