During a 30-hour Union bombardment of Fort Pulaski, Acting Brigadier General Quincy Adams Gillmore used his knowledge of the fort's strengths and weaknesses to direct artillery from Tybee Island against the angle aligned with the powder magazine. Rifled solid shots and exploding shells smashed through the fort's seven and one-half foot thick brick walls, proving that walls once considered unbreachable could not withstand the spinning projectiles of this new technology. Colonel Charles H. Olmstead surrendered the Confederate fort before incoming shells could explode the powder magazine and destroy the entire garrison. Observers saw the attack as evidence that rifled heavy artillery had transformed warfare and rendered traditional stone and brick fortifications vulnerable.