The armed trawlers or "bous"
In order to organize the Basque Auxiliary Navy, Egía selected the most appropriate vessels for each of the missions. Four cod fishing boats belonging to PYSBE, a company in Pasajes, brought to Bilbao after the evacuation of Guipuzcoa, were chosen to protect the merchant traffic and the fishing boats fishing in territorial waters. On 30th October 1936, the leader of the Basque Government, José Antonio Agirre, signed the decrees to seize the Hispania, Euzkal-Erria, Mistral and Vendaval, and it was up to the Republican Navy to arm them. Initially, one 101.6 mm gun was installed on the bow and 2 machine guns on the deck (the Mistral also had one 76.2 mm on the stern). On 9th December, they were rechristened Araba, Bizkaya, Gipuzkoa and Nabarra and between January and February, second 101.6 mm was installed on the sterns of all of them, except for the Araba. The Araba, whose boilers had always been in a very poor state, was disarmed in February 1937 and was taken to the dry dock to be completed refitted, which had not been completed when Bilbao fell in June.
In December, two small pair-trawling boats, the Goizeko-Izarra and the Iparreko-Izarra, were armed with one small 57-mm gun fitted on the bow and the Iparreko also had one machine gun. The Donostia trawler came into service in January. It had previously been the Virgen del Carmen trawler on Franco's side, but it crew mutined on the night of 5th to 6th December and took the vessel into Bilbao. Its original weapons were altered. 
A 76.2 mm gun, taken from the Gipuzkoa, was fitted to the bow, in addition to its existing 47 mm gun on the stern, along with 2 machine guns and 6 German depth chargers, which it also had when it came into Bilbao. In late spring 1937, work began to arm two more vessels, called Gazteiz and Iruña, but the latter was still been fitted out and neither was armed when Bilbao fell. Only the Gazteiz would come into service in June, but was unarmed. The people would popularly refer to these ships as “the bous”.
Minesweepers and auxiliary vessels
Small fishing vessels, were selected to act as minesweepers or “barreminas”. They were initially reduced in number, with no more than 6 being used for this task in January 1937, but the successive mining of Bilbao forced it to be increased in number until there were 24 in May 1937. At the start, these vessels would keep their original names, but they were removed in May and the ships were allocated the numerals D-1 to D-24. In general, they were ships between 30 and 110 tons, which could sail at speeds of 8 to 10 knots and with crews of 8 and 12 sailors. A total of 27 vessels were used as minesweepers by the Basque Navy at one time or another.
Six coastal fishing boats, which the Auxiliary Navy classified as “auxiliary motor boats” or “laguntzailles”, were used to support the minesweepers and for night surveillance. At the beginning of May, their names were replaced by the numerals L-1 to L-6. They were very small, 12 to 35 tons in size, had 4 to 10-man crews and could sail at 8 to 10 knots. Neither the minesweepers nor the motor boats were armed.
In addition to these, the Auxiliary Navy also had various auxiliary boats, yachts and fast motor launches. Some of them were used for harbourmaster tasks or the maritime link between Bilbao and Bayonne, and others worked with the minesweepers or to carry out various port tasks.
On the ships of the Cantabrian Sea Naval Forces
In May-June 1937, about 220 sailors from the Basque Sea Volunteers were sent on board the submarine C-6 and the destroyers José Luis Díez and Císcar, at the request of the Cantabrian Sea Naval Forces commandant, to replace other crew members who were under suspicion or to cover casualties. From then on, until the fall of Bilbao, the two destroyers and the submarine were supplied by the Quartermaster's Services of the Basque Navy Headquarters. Once the vessels were transferred to Santander, a good number of them were disembarked and the remainder joined to the Republican Navy.
