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 Nationalist destroyer Velasco attempted to intercept the armed trawlers Gipuzkoa and Bizcaia (still under their peacetime names of Mistral and Euzkal-Erría).

[2] 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.

[2] 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.

The armed trawlers Bizcaia, Gipuzkoa, Donostia and Nabarra tried to lure the rebel heavy cruiser Canarias to a point within firing range of the coastal batteries.

[3] 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.

[5][6][4] 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.