Basque Auxiliary Navy The Basque Auxiliary Navy ( , ) was a section of the Spanish Republican Navy operating in the Bay of Biscay between 1936 and 1937 . It began operations in October 1936 at the behest of the Basque Government . The main Basque naval base was at Portugalete . History . During the Spanish Civil War , the Second Spanish Republic had allowed an autonomous government in those Basque areas of Spain that had not been taken by the Nationalist faction , like Biscay and parts of Guipuscoa . The coast of Galicia , along with the Ferrol naval headquarters , became part of rebel - held territory early in the Spanish Civil War . When the Republican Navy became mainly confined to the Mediterranean Sea , after the failure of the blockade of the Gibraltar Strait , its operations in the Bay of Biscay were taken over by the Basque Auxiliary Navy . Basque Auxiliary Navy ships engaged mainly in minesweeping operations . They also played a key role in the evacuation of civilians who fled as the rebel armies advanced from coastal cities such as Gijón and Santander . The first naval action against Francoist forces took place on 15 November 1936 , when the rebel destroyer " Velasco " attempted to intercept the armed trawlers " Gipuzkoa " and " Bizcaia " ( still under their peace - time names of " Mistral " and " Euzkal - Erría " ) . The trawlers were steaming for Biarritz , France to escort a freighter when they were spotted by the warship 40 miles off Pasaia . In the ensuing battle , the " Velasco " was hit and limped away , while the " Gipuzkoa " received some damaged on her forecastle , with two seamen wounded . There was another encounter with the " Velasco " on 8 January 1937 , when the rebel destroyer was laying down mines along with the auxiliary minelayer " Genoveva Fierro " off Portugalete . After a brief exchange of fire , the Nationalist warships withdrew without accomplishing their mission . The Francoist navy , however , didn ' t give up and nine days later they set up a minefield successfully . On 17 January the Basque armed trawler " Goizeko Izarra " struck one of the mines and sank with all her crew of 17 aboard . The following day , while clearing the minefield , the minesweeper " Mari - Toya " hit another mine and also sank ; six men of her crew were lost . Two days later , after the intense work of other minesweepers , the area was declared safe . In February and April , the Nationalist navy laid down two new minefields off Bilbao , but the Basque navy neutralized the devices . The minesweepers disabled more than 200 naval mines during the campaign . The Basque auxiliary navy became a player in a series of conflicts between the Spanish Republic and Nazi Germany , when in December 1936 the German freighters " Pluto " and " Palos " were captured by the armed trawler " Bizcaia " . " Pluto " was releasead , but the " Palos " , which was carrying military supplies to the rebels , was taken to Bilbao , where her cargo was confiscated . The largest engagement involving the Basque navy was the Battle of Cape Machichaco , on 5 March 1937 , when four naval trawlers escorting the transport ship " Galdames " , " Bizcaia " , " Gipuzkoa " , " Donostia " and " Nabarra " , tried to lure the rebel heavy cruiser to a point within firing range of the coastal batteries . The operation was unsuccessful , ending with the sinking of " Nabarra " , the " Gipuzkoa " with her bridge shot way , and the other two trawlers scattered . The transport was eventually captured by " Canarias " . " Gipuzkoa " finally arrived at Portugalete in flames and " Bizcaia " headed for Bermeo , where she met the Estonian merchantman " Yorbrook " , previously captured by the " Canarias " , and forced her to make port . " Donostia " sought shelter in France . On 1 May 1937 , " Donostia " , " Bizcaia " and " Gipuzkoa " shelled the port of Bermeo , which had fallen to Italian Fascist troops the day before . The Basque Auxiliary Navy was still operational after the fall of Bilbao in June 1937 , moving away from Basque waters and setting its base in Santoña and Santander . Later , as the republic also lost those harbors , they operated in Asturias , the last Republican province in North - West Spain . Finally , following the occupation of Asturias by the Francoist armies in October 1937 , the Basque Auxiliary Navy ceased its operations . Some Basque sailors became prisoners , but most of them were able to reach France . Naval units of the Basque Auxiliary Navy . Naval Trawlers . The naval trawler s were usually cod fishing vessels , known in Spanish as " bous " , fitted with pieces of artillery . The " Donostia " was the former Nationalist unit " Virgen del Carmen " , which changed sides after being captured and diverted to Bilbao by some members of her own crew on 6 December 1936 .