Gulf Coast campaign The Gulf Coast campaign or the Spanish conquest of West Florida , of the American Revolutionary War , was a series of military operations primarily directed by the governor of Spanish Louisiana , Bernardo de Gálvez against the British province of West Florida . Begun with operations against British positions on the Mississippi River shortly after Britain and Spain went to war in 1779 , Gálvez completed the conquest of West Florida in 1781 with the successful Siege of Pensacola . Background . Spain officially entered the American Revolutionary War on May 8 , 1779 , with a formal declaration of war by King Charles III . This declaration was followed by another on July 8 that authorized his colonial subjects to engage in hostilities against the British . When Bernardo de Gálvez , the colonial Governor of Spanish Louisiana received word of this on July 21 , he immediately began to secretly plan offensive operations . Gálvez , who had been planning for the possibility of war since April , intercepted communications from the British at Pensacola indicating that the British were planning a surprise attack on New Orleans ; he decided to launch his own attack first . To that end , he concealed from the public his receipt of the second proclamation . Control of the lower Mississippi . On August 27 , Gálvez set out by land toward Baton Rouge , leading a force that consisted of 520 regulars , of whom about two - thirds were recent recruits , 60 militiamen , 80 free blacks and mulattoes , and ten American volunteers headed by Oliver Pollock . As they marched upriver , the force grew by another 600 men , including Indians and Acadians . At its peak , the force numbered over 1 , 400 , but this number was reduced due the hardships of the march by several hundred before they reached Fort Bute . At dawn on September 7 , this force attacked Fort Bute , a decaying relic of the French and Indian War that was defended by a token force . After a brief skirmish in which one German was killed , most of the garrison surrendered . The six who escaped capture made their way to Baton Rouge to notify the British troops there of the fort ' s capture . After several days ' rest , Gálvez advanced on Baton Rouge , only from Fort Bute . When Gálvez arrived at Baton Rouge on September 12 , he found Fort New Richmond garrisoned by over 400 regular army troops and 150 militia under the overall command of Lieutenant Colonel Alexander Dickson . After nine days ' siege , Dickson surrendered . Gálvez demanded and was granted terms that included the capitulation of the 80 regular infantry at Fort Panmure ( modern Natchez , Mississippi ) , a well - fortified position that would have been difficult for Gálvez to take militarily . Dickson surrendered 375 regular troops the next day ; Gálvez had Dickson ' s militia disarmed and sent home . Gálvez then sent a detachment of 50 men to take control of Panmure . He also dismissed his own militia companies , left a sizable garrison at Baton Rouge , and returned to New Orleans with about 50 men . Mobile . In early 1780 Gálvez embarked on an expedition to capture Mobile , which was one of the only major British military establishments left in West Florida ( the capital , Pensacola , was the other ) . Assembling 750 men at New Orleans , he sailed for Mobile on January 11 , reaching Mobile Bay on February 9 after being delayed by storms . He was joined on February 20 by a supporting force of 450 from Havana , but did not begin siege operations until March 1 . After 14 days of bombardment , Fort Charlotte ' s walls were breached , and its commander , Captain Elias Durnford , surrendered . Gálvez in the fall of 1780 sought to capture Pensacola , but his expedition was devastated by a major hurricane . Its tattered remnants made their way back to either Havana or New Orleans , and planning began again for an expedition in 1781 . British authorities in Pensacola had , when war with Spain was imminent , attempted to shore up West Florida ' s defenses , but the meager resources allocated to the region meant that General John Campbell , the military commander at Pensacola , had been able to do little to stop Gálvez ' s advance . By late 1780 he had received some reinforcements , and managed to recruit a significant force of local Indians to bolster Pensacola ' s defenses . The destruction of Gálvez ' s expedition emboldened him to attempt the recapture of Mobile . In January 1781 he dispatched more than 700 men under the command of the Waldecker Captain Johann von Hanxleden to go overland . This force was defeated when it attacked one of the forward Spanish defenses of Mobile , and Captain Hanxleden was killed . The attack prompted Spanish authorities in Cuba to enlarge to Mobile garrison . Pensacola . Gálvez and Spanish authorities in Cuba again launched an expedition against Pensacola in February 1781 . With forces that eventually numbered about 8 , 000 , Gálvez , assisted by Spanish and French naval forces , first blockaded the Pensacola harbor , and then began siege operations on March 9 . By April 30 the Spanish had successfully placed cannons that could fully attack the main Pensacola defenses . A lucky cannon shot hit the powder magazine in one of the outer defenses on May 8 , and the Spanish quickly capitalized , capturing the position . Realizing his position was no longer tenable , Campbell opened surrender negotiations the next day . The terms of capitulation included all of the British West Florida .