The Marine Corps played a small role in the Civil War (1861–1865); their most prominent task was blockade duty. As more and more states seceded from the Union, about a third of the Corps' officers left the United States to join the Confederacy and form the Confederate States Marine Corps, which ultimately played little part in the war. The battalion of recruits formed for the First Battle of Bull Run performed poorly, retreating with the rest of the Union forces. Blockade duty included sea-based amphibious operations to secure forward bases. In late November 1861, Marines and sailors landed a reconnaissance in force from at Tybee Island, Georgia, to occupy the Lighthouse and Martello Tower on the northern end of the island. It would later be the Army base for bombardment of Fort Pulaski. In April and May 1862, Union Marines participated in the capture and occupation of New Orleans and the occupation of Baton Rouge, Louisiana, key events in the war that helped secure Union control of the lower Mississippi River basin and denied the Confederacy a major port and naval base on the Gulf Coast.