Dry Tortugas National Park , Florida ( CNN ) -- Weather and time have inflicted more damage to Fort Jefferson than hostile cannon fire ever did . The crumbling citadel rises 40 feet from the turquoise water of the Gulf of Mexico , an outpost of a bygone era . Built on an island in Florida 's Dry Tortugas , 70 miles past Key West , the fort is being restored by a squad of craftsmen who spend three-week shifts there between hurricane seasons . A cocoon of mesh and scaffolding shrouds one section of its 8-foot-thick walls as they work . It 's a grueling job , but it 's one Dennis Wood , a mason from Massachusetts , says he 's glad to have . `` Things are slow today , you know , '' Wood said . `` Got a job offer to come down here for the winter , so we took it . '' Efforts to restore Fort Jefferson have been under way for about 30 years . The current phase received a boost from the economic stimulus bill that passed Congress in 2009 , which devoted $ 7 million to the project . But planners estimate another $ 13 million is needed , and that money has yet to be allocated . The six-sided fort , roughly the size of Yankee Stadium , was designed to protect shipping lanes through the Gulf of Mexico . Construction began in 1846 , but advancements in the science of artillery rendered it obsolete before it was finished . During the Civil War , the Confederacy never bothered to try to seize it from Union forces . The Union kept a garrison of about 2,000 men there and used it mostly as a prison for Confederate captives and deserters . It was n't until after the war that it received its most famous inmate -- Samuel Mudd , the Maryland doctor convicted of aiding Abraham Lincoln 's assassin , John Wilkes Booth , by setting his broken leg . Mudd served more than three years at Fort Jefferson before receiving a pardon in 1869 . The Army abandoned the fort in 1874 , but the islands served as a staging area for U.S. warships during the Spanish-American War in 1898 and housed a seaplane base during World War I . It takes a 2 1/2-hour ride on a catamaran ferry to get to Fort Jefferson . The installation and the surrounding national park draw about 52,000 visitors a year , according to the National Park Service . But more than a century and a half of hurricanes and salt air have taken their toll on the massive walls . The iron shutters that shielded the fort 's guns have expanded as they rust , cracking and displacing the surrounding walls . Wood , the six other masons and eight laborers who are working to restore Fort Jefferson were unemployed before this job , said Ken Uracius , the project manager for Enola Contracting Inc. , which is doing the work . Uracius estimates about 100 people see some sort of work from the project . `` I have boat captains , '' he said . `` I have people running the boat that brought you out here . I have brick makers , I have cement makers . '' Work has gone on periodically for the past 30 years and is likely to go on for many more . But the Park Service says it 's important to save a unique monument . `` If we lose Fort Jefferson , that 's it , '' said Kelly Clark , who oversees the reconstruction project for the Park Service . `` There are no other Fort Jeffersons . ''
Work on Fort Jefferson , 70 miles past Key West , began in 1846 . Because of advances in artillery , the fort became obsolete before it was even finished . Though never attacked in wars , hurricanes and salt air have taken their toll . An estimated 100 jobs have been generated by $ 7 million worth of stimulus funds .