The ships were ordered in 1926 and were based on the British County-class cruisers. The designer was Sir Phillip Watts. These ships had anti-torpedo bulges and a slightly narrower beam as well as more powerful machinery. The boiler rooms were re-arranged compared to the British design and trunked into a single massive funnel rather than three funnels used on the British cruisers. The Spanish ships had a stronger secondary armament and although the original design included a catapult for a seaplane this was never installed.
Both ships were making their final sea trials when seized by the Nationalist side in the Spanish Civil War. Both of them were fitting out and completed with makeshift fire control and secondary armament.
Canarias was the flagship of the Nationalist Navy and sank 34 ships including the Republican destroyer Almirante Ferrándiz and the Soviet merchant Komsomol. She also damaged the destroyer José Luis Díez, forcing her to seek refuge at Gibraltar. During World War II she took part in the search of survivors from the German battleship Bismarck.
Baleares was completed without 'Y' turret, which was retrofitted in 1937. In September 1937 she engaged two Republican light cruisers in the Battle of Cape Cherchell. During a raid on Palma de Majorca in March 1938 she was intercepted by Republican destroyers and torpedoed by the destroyer Lepanto. The torpedoes blew up the forward magazines, disintegrating the fore part of the ship. The stern half remained afloat and 372 of her crew of 1221 were saved by British destroyers Boreas and Kempenfelt. 786 men died during the action.