Mutinous sailors on the Jaime I

This photograph of sailors on the battleship Jaime I was taken by Gerda Taro in 1937. It gives a sense of the special way in which the military revolt affected the Spanish navy.

Unlike officers in the Army and Air Force, who were divided in their loyalties, the vast majority of naval officers supported the coup of July 18. This led to dramatic situations onboard as most non-commissioned officers and ordinary crewmen, recruited among fishermen and men with other modest backgrounds, held left-wing political views. In general, if a ship was at sea when the coup began, or set sail immediately afterwards, rebel officers were arrested - and often executed. 355 naval officers were killed by Republicans. Such events were most frequent and bloodiest at the base in Cartagena, where the battleship Jaime I arrived in August after a voyage from the Cantabrian Sea.

In contrast, when ships were in rebel-held ports, they were boarded, and their crews subdued by anti-government forces who quickly undertook their own repression. The rebels murdered 8 officers, including two admirals, as well as 146 other ranks, most in El Ferrol. The Francoist repression continued after the war. Sailors who had been repatriated from Bizerta (Tunisia), where the Republican fleet had taken refuge shortly before the final defeat, were particular targets.

It has often been noted that while the majority of the fleet remained loyal to the Republic, the rebels were able to use their ships more effectively. This type of analysis must be qualified.

In 1936, the Spanish navy was third-rate, at best. It had only a few ships, and many of those were outdated. Most of the cruisers, destroyers, and submarines remained loyal to the Republic, but the execution of so many officers undermined their effectiveness, especially outside the Mediterranean where the Republic had no bases. Any initial advantage the Republic might have had was eliminated once the rebels launched two modern cruisers, the Canarias and Baleares, whose construction was in its final stages when the war began. Together with the support, sometimes tactical and sometimes direct, of the German and Italian navies, as well as  superiority in the air during most of the war, this seriously reduced the actions of the Republican fleet. (The Jaime I itself was attacked from the air repeatedly.) It also allowed the rebels to go on the attack, including blockading Republican ports.

Even so, the Francoists lost two capital ships in combat, the España and Baleares, while the Republic lost only some smaller vessels and the Jaime I. It was not destroyed in combat however. An onboard explosion while it was undergoing repairs in Cartagena killed some 300 sailors. The cause was never determined.