[2] In September 1937, the ship, bound to Barcelona from Odessa, was diverted by her captain and part of the crew towards Cagliari, Sardinia, where the Nationalists had an improvised naval base with the support of Fascist Italy.

After seeing some activity as a supply ship, Mar Negro was converted into a naval unit at the same shipyard where she and her sister had been built, the SECN facilities on the Nervion River, near Bilbao.

[2] Between 19 and 22 December 1938, Mar Negro seized three Greek steamers in short succession near the channel of Sicily; the tanker Atlas, and the freighters Aris and Oropus, without opposition of non-intervention forces.

[4] On 28 January 1939, the Nationalist cruiser shelled Palamós, one of the last Republican-held ports in Catalonia, scoring several hits on a British freighter and damaging some shore facilities.

[5] Spanish Republican sources say that the only British steamer at Palamós at the time was the largely disabled Lake Lugano, damaged by a flying boat attack on 6 August 1938 and later beached outside the docks.

Admiral Moreno, commander in chief of the Nationalist fleet, also played down the scale of the operation during a private meeting with the British consul at Palma de Mallorca.

Mar Negro's commander reacted quickly: a prize crew of 13 men was dispatched by boat to board the British cargo ship, after the auxiliary cruiser got close to Stangate.

The officer in charge of the party, after realising that the ship was now crewed by the Spaniards, communicated the news to his superior, who eventually conceded the capture.

A stand-off ensued, which ended abruptly at 8:30 pm when the British cargo ship, according to the Spanish version, attempted to ram Mar Negro.

The vessel had been captured in February off Cap de Creus by the Nationalist gunboat Dato, which was patrolling Catalonia's coast from Palamós to the French border assisted by the minelayer Vulcano.

[19] The cargo ship and her crew were held by the Spanish authorities several weeks after the end of the war at Palma,[20] where she remained under the supervision of the British consul until her release.

Meanwhile, on the political front, secret negotiations between Franco and Colonel Casado, a Republican leader who had formed the National Defence Council to replace the government after a coup against the communist party, were going on.

Franco gave unwritten assurances that he will not ordered the occupation of Madrid to his army before the main Republican anti-communist leader came to exile.

[12] On 26 March there were three minor incidents with units of the French Navy, and on the 27 the cruiser successfully protected a Nationalist flying boat which was being chased by the still active Republican air force.

They took control of the port and the hulls of the Spanish steamer Vicente, of 534 tons, the British Dellwyn of 1,420 and a dredger, all of them sunk in shallow waters by earlier air attacks.

[25] Before returning to Gandía and get some time to rest, the auxiliary cruiser made a full reconnaissance of the small ports of Denia and Jávea.