Rear Adm. Samuel F. Du Pont ordered three ironclads—USS Patapsco, Passaic, and Nahant— to test their guns and mechanical appliances and practice artillery firing by attacking the Confederate defenses at Fort McAllister, then a small three-gun earthwork battery. One of his goals was to determine how effective fire from the monitors' big guns would be against an earthen shore battery.
On March 3, 1863, the three ironclads conducted an eight-hour bombardment. The bombardment did not destroy the battery, but it did some damage, while the three ironclads received some scratches and dents from return fire from the fort. The tests were helpful for knowledge and experience gained, but Fort McAllister did not fall, showing that the ironclads’ firepower alone could not destroy an earthen fort.