15. Heavy bombardment of the position was to precede a series of assault waves
Gillmore decided to repeat his success at Fort Pulaski through a lengthy bombardment of the fortification using both land-based and naval guns. Among the 11 ships assigned to the bombardment was USS New Ironsides, a sail and steam-driven ship with an armor-plated hull which carried, among other cannon, fourteen 11-inch Dahlgren guns. In April 1863, the ship had been one of nine which bombarded Fort Sumter for several hours with little effect. Gillmore believed that the bombardment of Fort Wagner would be more effective. Gillmore was unaware of the garrison’s ability to shelter in the bombproof.
As additional protection, the Confederate garrison had prepared sandbags with which to cover the guns within the bastion, withdrawing the majority of the garrison in the bombproof, secure in the knowledge that any bombardment would have to be lifted once an infantry assault was launched. Had Strong used a bombardment prior to his assault on July 11 (he hadn’t, relying on surprise and the fog) this tactic may have been revealed. As he prepared for his second assault on Fort Wagner he planned a series of assaults, each launched to support its predecessor, in order to carry the fort following a lengthy bombardment.