Heavy caliber rifled cannon which the Federals needed to reduce Pulaski had arrived nearby in February, at which time Gillmore decided to locate the batteries at the northwestern tip of Tybee Island nearest the fort. By March, Gillmore was offloading siege materiel onto Tybee Island. Roads had to be laid down, gun emplacements excavated, magazines and bomb-proofs constructed. As the work progressed southwesterly nearing the Fort, in the last mile the Union troops came under fire from the Fort's Confederate gunners. A ranging shot said to be aimed by Colonel Olmstead himself cut a Union soldier in two. The following bombardment from elevated fort guns effected mortar barrages that forced all construction to proceed on Tybee Island by night. Each morning the uncompleted elements of siege construction were camouflaged against the fort's spotters.