Rear Admiral William T. Sampson had been chasing a rumor. American intelligence believed that Admiral Pascual Cervera y Topete's Spanish fleet was steaming from the Cape Verde Islands toward Puerto Rico, and Sampson sailed from Key West on May 2 with a formidable squadron -- battleships, armored cruisers, monitors, torpedo boats, and a pair of unarmed yachts carrying press correspondents and officials along to watch what was expected to be a decisive naval engagement. The fleet paused at Cap-Haitien on May 8 for telegraphed orders that never arrived with new information. In the days before reaching San Juan, the auxiliary cruiser Yale skirmished with a better-armed Spanish vessel off the harbor and briefly exchanged fire with Fort San Cristobal. None of it revealed Cervera's location, because Cervera was not there. He had sailed for Santiago de Cuba instead. Sampson would not learn this for another six days. In the meantime, he had a fleet, he had orders, and he had a city in front of him.

Sampson's plan was cautious: Detroit would lead the battle line into the bay, and the fleet would fire only if fired upon. But events outran orders. Detroit steamed too far forward, the other ships followed, and when Sampson could not recall them, he ordered Iowa to train her guns on El Morro. Iowa fired a single shot into the water -- a feint. The Spanish, believing themselves under attack, opened fire from the ancient fortress. Iowa answered with a broadside that reportedly blew away a portion of the castle walls. From five until eight that morning, the American fleet circled in the harbor mouth, firing from port and starboard guns. Rough seas and high winds threw rounds off target on both sides, and that mattered profoundly -- because El Morro and San Cristobal sat within the city itself. Shells that missed the fortresses struck San Juan's houses and churches. At least one round hit the 16th-century San Jose Church. The Navy fired 1,360 shells in three hours. The Spanish, outgunned with older Ordonez cannon and obsolete banded howitzers, managed 441 rounds in reply.

When the guns fell silent at eight o'clock -- the monitor Terror continued firing alone until 8:30, having failed to receive the cease-fire order -- the accounting began. Five Puerto Rican civilians had been killed and eighteen wounded. Two Spanish soldiers were dead, thirty-four more injured. On the American side, one sailor aboard New York was killed in action, with a handful of wounded across two ships. A gunner's mate on the monitor Amphitrite died of heat exposure in a barbette. The toll in stone was harder to quantify. The civilian buildings damaged stood adjacent to El Morro, caught in the corridor of fire that made a miss on the fortress a hit on someone's home. A French cruiser, the Amiral Rigault de Genouilly, sitting in the harbor on a peacetime visit, took stray hits to its smokestack and rigging -- a diplomatic embarrassment that likely restrained Sampson from targeting the small Spanish gunboats sheltering nearby. By afternoon the American fleet had withdrawn, steaming back toward the Havana blockade. San Juan was left with its dead, its damaged buildings, and the knowledge that the war Spain was losing would soon change everything about the island.

The bombardment lasted three hours and decided nothing militarily. Sampson did not capture San Juan. He did not find Cervera's fleet. He did not even destroy the harbor defenses -- El Morro and San Cristobal stood, battered but functional. The engagement's significance was something else entirely: it was the first major action of the Puerto Rican Campaign, the opening announcement that the United States intended to take the island from Spain. The Treaty of Paris, signed that December, made it official. Puerto Rico passed from one empire to another, its residents offered no voice in the transfer. The residents who fled through the city gates that May morning -- whose numbers were so large that the streets emptied almost completely -- had understood something instinctively. This was not a battle between armies. It was a rearrangement of power conducted over their heads, and the shells falling on their homes were the punctuation marks. The fortresses they had lived beside for centuries, built to protect them from exactly this kind of assault, had become the very targets that drew fire into their neighborhoods.