Caamaño was awarded the Cruz de la Orden de Merito Naval Primera Clase (The Cross of the Order of the Naval Merit 1st class) by the Spanish government for his role in the rescue of the cargo of the SS Antonio López,[note 1] a Spanish transoceanic steamer.

[1] On May 8, 1898, the USS Yale captured a Spanish freighter, the Rita in San Juan Bay, this being the first hostile encounter between the warring sides in Puerto Rico.

On May 9, Yale fought a brief battle with an auxiliary cruiser of Spain, name unknown, resulting in a Spanish victory.

[1] For weeks, the United States Navy had been awaiting the arrival of the Spanish fleet under Admiral Pascual Cervera y Topete, unaware that he had already eluded them and slipped his squadron into the Bay of Santiago.

[3] On May 12, U.S. Admiral William T. Sampson and a fleet of ten American ships arrived in San Juan to bombard the city's citadels.

[7][failed verification] On 15 July, USS New Orleans arrived to relieve Yosemite, and the next day it quickly finished off the "SS Antonio Lopez" by firing twenty incendiary shells into the vessel and sinking it.

Though the Antonio Lopez had been sunk, she successfully delivered her cargo, ensuring that any American assault on San Juan would be met with stronger resistance.

[1] The residents of San Juan were furious with Rivero and blamed him for the destruction caused to their city by the American bombardments, however nothing came of those accusations.

Rivero-Méndez was ordered to turn over the keys of all the military installations in San Juan to Captain Henry A. Reed of the U.S. Army after the Treaty of Paris of 1898 was signed.

By October 18, the Spanish withdrawal from Puerto Rico was completed as the final troops left San Juan for Spain.

Later that same year he was named director of the Laboratorio y Centro Electrónico de Artillería (Laboratory and Electronic Center of Artillery).