Fort Pickens was a United States military post on Santa Rosa Island near Pensacola, Florida. It remained under federal control throughout the American Civil War (1861-1865). When Florida seceded (withdrew) from the Union in January 1861, Lieutenant Adam J. Slemmer moved a small body of federal soldiers into Fort Pickens. Union and Confederate authorities agreed that the Union would not reinforce the fort, and the Confederate States would not attack it. But after Confederate forces fired on Fort Sumter, South Carolina, on April 12, 1861, and the war began, the Union rushed reinforcements to Fort Pickens. The defenders of the fort withstood a surprise attack on Oct. 9, 1861.