After the repulse of July 18, Gillmore decided to reduce Wagner by siege approaches and to begin bombarding Sumter at the same time. His position was close enough to the latter work to allow Parrotts to strike the masonry walls. It was believed that the siege approaches might not have to be run all the way to Wagner, for if Sumter's guns could be dismounted, the navy might be able to run in and cut off boat communication between Charleston and Morris Island. This would accomplish a complete investment of Wagner and starve the garrison into surrender.1
The result was one of the classic siege operations of the Civil War. The reduction of Battery Wagner was the largest, most significant offensive against Charleston. It involved the use of several modern devices, from land mines to calcium lights, and was directed by a gifted engineer who also served as commander of the Federal army conducting the siege. The Confederate defending force was badly outnumbered and nearly cut off from the outside world, but it held Wagner for two months under conditions that became appalling.
While Gillmore continued to act as his own engineer, he had several engineer officers to supervise the construction of works. Col. Edward Wellman Serrell, Maj. Thomas Benton Brooks, and Lt. Peter S. Michie were among the best engineers in the Union army. Serrell and Brooks had been commissioned in the 1st New York Engineers. The latter was put in charge of the saps and the batteries that supported them.2
For his part, Beauregard fully realized what was to come. "Contest here is now one of engineering," he wrote Adj. Gen. Samuel Cooper in Richmond. "With sufficient time, labor and long range guns, our success is probable, owing to plan of defense adopted. Otherwise, it is doubtful in proportion to the lack of those three elements." To that end, Beauregard ordered Wagner to be held until its parapet was so badly damaged it could no longer protect the garrison, and then the infantry was to defend each sand hill between Wagner and Gregg. The latter work could hold out for a few days on its own, he thought. Like Gillmore, Beauregard was a fine engineer, and he had a slate of good subordinates under him. Col. David B. Harris headed a contingent of