United States Fourth Fleet U . S . Fourth Fleet is a United States Navy command operating the Navy component command of U . S . Southern Command ( USSOUTHCOM ) . Fourth Fleet is headquartered on Naval Station Mayport in Jacksonville , Florida and is responsible for U . S . Navy ships , aircraft and submarines operating in the Caribbean , and Atlantic and Pacific Oceans around Central and South America . Mission . U . S . Naval Forces Southern Command ( USNAVSO ) and U . S . FOURTH Fleet supports USSOUTHCOM joint and combined full spectrum military operations by providing principally sea based , forward presence to ensure freedom of maneuver in the maritime domain , to foster and sustain cooperative relationships with international partners and to fully exploit the sea as maneuver space in order to enhance regional security and promote peace , stability , and prosperity in the Caribbean , Central and South American regions . History . U . S . FOURTH Fleet was a major U . S . Navy command in the South Atlantic Ocean during World War II . It was originally established in 1943 to protect the U . S . against raiders , blockade runners and enemy submarines . In 1950 , U . S . FOURTH Fleet was disestablished when responsibilities were taken over by U . S . SECOND Fleet . On April 24 , 2008 , then Chief of Naval Operations ( CNO ) Adm . Gary Roughead announced the reestablishment of U . S . FOURTH Fleet . Nearly three months later on July 12 , 2008 , he reestablished U . S . FOURTH Fleet during a ceremony at Naval Station Mayport , Florida . U . S . FOURTH Fleet headquarters is co - located with USNAVSO headquarters in Mayport , Fla , and is commanded under a two - star Admiral . Commander , USNAVSO ( COMUSNAVSO ) retains missions as the Navy component commander for USSOUTHCOM . U . S . FOURTH Fleet is responsible for U . S . Navy ships , aircraft and submarines operating in the USSOUTHCOM area of responsibility , which encompasses the Caribbean , Central and South America and surrounding waters . As part of the reestablishment , no new permanently stationed vessels will be assigned to U . S . FOURTH Fleet , as it is an organizational fleet staffed to fulfill a planning and coordination mission . U . S . FOURTH Fleet will be focused on strengthening friendships and partnerships and will have five missions : support for peacekeeping , Humanitarian Assistance , Disaster Relief ( HADR ) , traditional maritime exercises , and counterdrug support operations . Reaction to reestablishment . This reactivation , without informing regional governments , sparked concern within some South American governments . The governments of Argentina and Brazil made formal inquiries as to the fleet ' s mission in the region . In Venezuela , President Hugo Chavez accused the United States of attempting to frighten the people of South America by reactivating the fleet and vowed that his country ' s new Sukhoi Su - 30 jets could sink any U . S . ships invading Venezuelan waters . Cuban ex - president Fidel Castro warned that it could lead to more incidents such as the 2008 Andean diplomatic crisis . Fourth Fleet Ships . No ships are permanently assigned to the Fourth Fleet . Ships homeported in the United States Fleet Forces Command and United States Third Fleet routinely deploy to the Fourth Fleet area of responsibility ( AOR ) , during which time they are under the operational control of the Fourth Fleet Commander . This is consistent with ships deploying to the other numbered fleets ( Fifth , Sixth , and Seventh Fleets ) , although all of those fleets have at least one permanently assigned ship .