On a ledge 40 feet above the Mississippi, the Confederates in March, 1863 , laid out Fort Cobun. Protected by a parapet nearly 40 feet thick were four big guns manned by Company A, 1st Louisiana Heavy Artillery. The guns of Fort Cobun under command of Captain John B. Grayson fired their first hostile shots on March 31 at Admiral David G. Farragut's squadron as it passed down river. On April 29, seven of Admiral David D. Porter's gunboats attacked the Grand Gulf fortifications. For more than five hours, the Union ironclads and the guns of Fort Cobun dueled. The Confederate artillerists disabled the "Tuscumbia". Unable to knock out the Confederate guns, the Union gunboats broke off the bombardment.
Following the occupation of Grand Gulf, Admiral Porter said, "Grand Gulf is the strongest place on the Mississippi."