Third Battle of San Juan ( 1898 ) The Third Battle of San Juan began on 28 June 1898 when an American auxiliary cruiser intercepted a Spanish blockade runner . A Spanish squadron attempted to rescue the blockade runner and succeeded in taking off supplies and her crew but failed to save the ship , which the American warship engaged and forced to run aground . Prelude . Puerto Rico had been under attack by US Navy forces under the command of Rear Admiral William T . Sampson since just before the Bombardment of San Juan early on in the war . The only Spanish effort to break the blockading forces had failed on 22 June , and instead of actively engaging the Americans the Spanish forces were bottled up in harbor at the capital of San Juan . Blockade runner s had on occasion slipped through the San Juan Blockade , but were often driven away or captured before ever nearing the harbor . The SS " Antonio Lopez " was a transport turned blockade runner that had been disarmed and fitted out at Cadiz , Spain and set sail on June 16 for San Juan with a large supply of cargo , food , and twelve modern artillery pieces to bolster the defense of San Juan . On 28 June , she was met by the American auxiliary cruiser which had just relieved the as the blockading ship off San Juan . The auxiliary cruiser was crewed by members of the Michigan Naval Militia and commanded by William Emory . Battle . With the blockade runner in sight , " Yosemite " began chase and opened fire on the vessel firing a shot . " Antonio Lopez " wasted no time and began to flee towards the protection of San Juan ' s Fort San Felipe del Morro and Fort El Cañuelo while " Yosemite " kept up its fire upon the vessel . As she was running for San Juan , the blockade runner became up on a reef , as the captain was quite unfamiliar with the waters in the area . Unable to free his vessel and taking casualties , the captain of the Spanish vessel ordered his crew to abandon ship . As the American vessel closed in on her prey , the Spanish forts opened fire and Emory began zig - zagging in order to avoid taking their fire . In an effort to save the " Antonio Lopez " and its much needed cargo , the Spanish squadron , bottled up in the harbor , sortie d out to rescue her . The Spanish gunboats and " Ponce de Leon " and the cruiser rushed to the blockade runner ' s aid and attacked the approaching American cruiser . As soon as the American vessel was in range , the forts opened fire . The Spanish cruiser ' s fire temporarily drove off " Yosemite " , but the American auxiliary cruiser soon returned and managed to force " Isabell II " and " General Concha " to the protection of the coastal forts while " Ponce De Leon " hid behind the burning " Antonio Lopez " . Under the protection of the Spanish forts and vessels , the blockade runner was unapproachable by " Yosemite " and with the Spanish transport on fire and effectively neutralized she moved back to her blockading position . " Yosemite " had done her job effectively though , and " Antonio Lopez " was stranded on the reefs and could not be dislodged , despite strenuous Spanish efforts to do so . Aftermath . With a renewed attack by " Yosemite " looming , the Spanish under the command of Captain Ramón Acha Caamaño were quick to remove as much of the stranded ship ' s cargo as possible . Their desperate efforts proved fruitful in that they were able to salvage nearly the entire cargo from the hulk . They left behind only some minor articles and one cannon that had fallen overboard during salvage operation . On 15 July , arrived to relieve " Yosemite " , and the next day it quickly polished off " Antonio Lopez " by firing twenty incendiary shell s into the vessel , sinking it . Though " Antonio Lopez " had been sunk , she had successfully delivered her cargo , ensuring that any American assault on San Juan would be met with stronger resistance . Today , the wreck of the SS " Antonio Lopez " is a National Historic Landmark and a public dive site .