The Basque Auxiliary Navy (Spanish: Marina de Guerra Auxiliar de Euzkadi, Basque: Eusko Itsas Gudarostea) 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.