MV Mar Negro The Auxiliary cruiser Mar Negro was an armed merchantman of the Nationalist Spanish navy during the Spanish Civil War . The cargo ship was launched in 1930 along with her sister ship " Mar Cantábrico " , and after five years on the " Compañía Marítima Del Nervión " company , she was first requisitioned by the Spanish Republican Navy in 1936 . Captured by a group of Nationalist sympathizers from her crew off Algeria in 1937 , she entered in service in 1938 after being converted to an auxiliary cruiser . Civilian career . The " Mar Negro " was built in 1930 along with her sister ship . She was a 6 , 632 - ton motor vessel and was part of a series of four ships of different tonnage . Two of them were 4 , 700 - ton steamers ( " Mar Blanco " and " Mar Caribe " ) , while " Mar Negro " and " Mar Cantábrico " were propelled by two diesel engines . The merchantmen were owned by the " Compañía Marítima del Nervión " , based at Bilbao . The cargo vessels were engaged in trade between Spain and US ports at the Gulf of Mexico . Both of them would ended up as auxiliary cruisers of the Nationalist navy . Under Republican flag . At the beginning of the war in 1936 , " Mar Negro " was moored at Barcelona , a city which remained under the control of the Government . She was fitted out as a troop transport , and was one of the Republican ships which took part of the ill - fated landing on Mallorca on August 1936 . Months later , she became involved in the maritime traffic between the Soviet Union and the Spanish Republic , and survived the attack of an Italian submarine . Career as Nationalist auxiliary cruiser . 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 Nationalist had an improvised naval base with the support of Fascist Italy . After seeing some activity as a supply ship , the merchant 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 . She was equipped with four 152 mm main guns , four 88 mm , four 47 mm Armstrong , three 20 mm Scotti and three depth - charge launchers . Completed on May 1938 , the auxiliary cruiser joined the maritime blockade on Republican ports in the Mediterranean . Between 19 and 22 December 1939 , the " 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 . She landed the 105 Infantry division on Mahón , Minorca , after the Republican surrender of this island , on 9 February 1939 , with the support of the minelayer " Júpiter " . After the fall of Catalonia , she led a naval parade off Tarragona with General Franco aboard on 22 February 1939 . She took part of the aborted landing on Cartagena on 6 March , when she assisted the " Mar Cantábrico " in the rescue of a German flying boat damaged by Republican aircraft and the capture of an armed tug . End of the war . On 8 March 1939 , Franco ’ s government decreed a ban on shipping around three miles from the coast of Levante , between the ports of Adra and Sagunto . After objections from the British government , the Nationalists soften this declaration by replacing the word “ ban ” for “ restrictions ” to shipping . 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 . Indeed , the Nationalist deployment was reduced to submarine patrols around Cartagena and the presence of an auxiliary cruiser and a destroyer off Valencia . In the last case , there was a rotation between the auxiliary cruiser " Mar Cantábrico " and " Mar Negro " and the old destroyers " Ceuta " and " Melilla " . Incident with HMS " Sussex " . On 16 March 1939 , two incidents between the " Mar Negro " and the British heavy cruiser HMS " Sussex " took place off Valencia , with the result of a British steamer captured and another damaged . The Spanish auxiliary cruiser also suffered some scratches on her stern in the aftermath . The " Mar Negro " and the Italian - built World War I destroyer " Melilla " were enforcing the blockade outside Valencia ’ s port . Shortly before the departure of " Melilla " back to Palma for refueling , they spotted a cargo ship steaming for Valencia . She was the British freighter " Stangate " , of 1 , 289 ton . At 10 : 00 AM , while clearing for action , the cruiser ’ s commander warned the vessel that she will be fired on if she enters Spanish waters . Apparently ignoring the threat , " Stangate " was within the three miles limit by 10 : 30 . The vessel was maneuvering near the beach of Saler , where the Republicans had mounted a 381 mm battery , which kept silent during the incident . Then " Mar Negro " ’ s commander ordered the merchantman to stop , but her captain steered to the east , toward international waters . The " Stangate " eventually came to a stop outside the three miles , approximately at . At the same time , the British cruiser HMS " Sussex " appeared on scene . " 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 the " Stangate " . The merchant was then taken under control by the Nationalist warship . " Sussex " ’ s commander requested an explanation regarding the position of " Stangate " at the time of her capture , and sent a party on board the British vessel . The officer in charge of the party , after realising that the ship was now manned by the Spaniards , communicated the news to his superior , who eventually conceded the capture . The " Stangate " was then driven to Palma by the prize crew at 2 : 00 PM . During the evening of that day , while on patrol off Sagunto , the " Mar Negro " spotted another British steamer , the " Stanhope " , just outside territorial waters . Nevertheless , the " Mar Negro " ordered the ship to stop , on the basis that the merchant had departed from Valencia , thus breaching the restrictions on shipping around the three miles zone . The captain of the merchantman refused to submit , and made a distress call to HMS " Sussex " . A stand - off ensued , which ended abruptly at 8 : 30 PM when the British cargo , according to the Spanish version , attempted to ram " Mar Negro " . The Nationalist warship maneuvered to port to avoid the collision , but the port bow of the merchant bounced her port quarter off . The incident resulted in some damaged on both ships . All units involved fled the scene afterwards , the " Stanhope " with the help of HMS " Sussex " . The " Mar Negro " was also mentioned in the House of Commons on 20 March 1939 in connection with the confinement of seven British subjects on board the cruiser . They were members of the crew of the small British steamer " Stangrove " , of 550 ton . The vessel had been captured in February off Cap de Creus by the Nationalist gunboat " Dato " , which was patrolling Catalonia ’ s coast from Palamos to the French border assisted by the minelayer " Vulcano " . The " Stangrove " was sent first to Barcelona and then to Palma , where she was lost under suspicious circumstances , wrecked by a gale . Her master , Captain William Richards , died in the incident . The ship was saved by the Spanish right after the war , and subsequently renamed " Castilla del Oro " and later " Condestable " . The " Stangate " was the last merchantman captured at high seas during the Spanish civil war . The cargo ship and her crew were held by the Spanish authorities several weeks after the end of the war at Palma , where she remained under the supervision of the British consul until her release . Fall of Gandía . On 25 March 1939 , " Mar Negro " rotated duties with her sister ship " Mar Cantábrico " as usual . Meanwhile , on the political front , secret negotiations between Franco and Colonel Casado , a Republican leader who had taken control of the government after a coup against the communist party , were going on . These talks included the mediation of the British consul at Valencia , Mr . Godden . 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 . The agreement also implied the evacuation by sea of a large number of Republican sympathizers from the port of Gandia , south of Valencia . The British manager of this port , a Mr . Apfel , was a key figure in the rescue of refugees , who were taken a board the British cruisers HMS " Galatea " and HMS " Sussex " , as well as the hospital ship " Maine " and several freighters . Conversely , the deal allowed the repatriation of Italian prisoners still held by the Republicans in British ships bounded for Palma . Indeed , just hours before her replacement by " Mar Negro " , the " Mar Cantábrico " stopped and searched the London - registered " Stanland " , but following orders from the Nationalist high command the auxiliary cruiser allowed her to proceed to Valencia . 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 . The enemy aircraft were forced to disengage by the 88 mm guns of the " Mar Negro " . On 29 March , the cruiser headed for Gandía , where the evacuation sanctioned by Franco was taking place . After the last refugee was on board the British vessels , a party of 22 men , led by the 2º commander of the " Mar Negro " landed in a boat . They took control of the port and the hulls of the Spanish steamer " Vicente " , of 534 ton , the British " Dellwyn " of 1 , 420 and a dredger , all of them sunk in shallow waters by earlier air attacks . The cargo ships were later raised and put in service under Spanish Nationalist flag , the " Dellwyn " under the name " Castillo Montesa " . 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 . On 31 March they informed to the British consul , after a request by the commander of HMS " Galatea " , that all Spanish ports were open to British shipping . The " Mar Negro " eventually returned to civilian service on October 1939 , seven months after the war was over .