At 5:30 AM on the morning of April 10th, First Lieutenant James H. Wilson rowed to Fort Pulaski from Big Tybee Island in a dingy with a small crew. Upon arrival he delivered a surrender ultimatum. The garrison commander, Colonel Charles H. Olmstead of the 1st Georgia Infantry regiment, rejected it. At 8:15 AM First Lieutenant Horace Porter fired the first shot from a 13-inch mortar at Battery Halleck. Soon the remaining batteries were bombarding the fort.
          Several of the carriages for the guns malfunctioned during the day, but engineers repaired them and all were back in action by the next day. The large rifles blasted the walls and created deep gouges. However, the large smoothbore cannons and the mortars were a disappointment. The smoothbore cannons did not chip away as much bricks as the rifles, and the mortars proved too inaccurate to be effective. In addition, the members of the 46th New York Infantry working the guns at Battery Sigel became unmanageable. The commander of the regiment, Colonel Rudolph Rosa, continually disregarded orders and could not control his men. General Gillmore ordered him away from the battery, and his men refused to work without him. They too were relieved and a detachment from the 8th Maine Infantry and sailors from the U.S.S. Wabash manned the battery the next day. Still, by the end of the first day the Union guns had damaged the fort more than they could observe. Fire from the rifled cannons had shot away much of the two casemates in the southeast corner, and dismounted most of the barbette guns that could face Goat Point from their carriages.
          The bombardment continued the next day. The fire of the cannons was concentrated on widening the damage to the angle between the south and southeast wall. Only three Confederate guns could return fire. The effect of the concentrated fire on a single section of the fort was spectacular. Showers of bricks flew through the air with every hit. The holes in the casemate openings widened, and large sections of the fort crumbled and fell into the moat. With each hit the breach widened. Work began on scaling ladders; the plan being to assault the fort on the night of April 12th if enough boats could be made available for the necessary troops.
          During mid-morning a Confederate shell exploded in Battery McClellan, killing Private Thomas Campbell of Company H, 3rd Rhode Island Artillery. This was the only fatality of the battle.
          With the breach widening with every hit, Union shells began to pass through hole, over the parade ground, and strike the opposite northern wall. The northern magazine was located in this northwestern corner. Even though the magazine was protected by a thick wall, one shot eventually exploded in the entry way. Colonel Olmstead realized it was only a matter of time before Union shells breached the magazine and exploded, with devastating results to the garrison. At 2:00 PM he ordered a white flag raised over the fort. The Federal batteries ceased firing and cheers erupted up and down the beach as the Union gunners celebrated their victory. General Gillmore himself went to the fort and arranged the surrender.  Fort Pulaski had fallen, and Savannah was cut off from the sea.