 Complete the following phrase:  The Blockade Strategy Board had recommended that Ship Island, which lies in the Gulf between Mobile and New Orleans, be taken and used as a base for the West Gulf Blockading Squadron. This was easily done, as on September 16, 1861, it was abandoned by its Rebel defenders, who feared that they might be cut off from the mainland. Their fears were justified; the next day, arrived and offloaded Federal troops to take possession. Almost immediately, however, the island was transformed from base and coaling station to a more important function; it became the staging area for the approaching attack on the Mississippi River 