[3] After the triumph of the uprising of July 18, 1936 in Navarre, mainly thanks to the Carlist component, the raised requeté regiments (tercio) were made part of the army's structure.

[4] On December 6, 1936, General Emilio Mola ordered that the nationalist Army's 6th Division [es] be divided into two Groups: the first would cover the entire Basque front from Ondarroa to Orduña and the second from this point to the limits of the provinces of León and Palencia.

Biscay and the north represented the majority of Spanish heavy industry and taking it over would close one of the fronts, making it decisive for the Nationalists' victory in the war.

General Mola's plan consisted of cutting the Basque Country in a southeast–northwest line with the four[n. 1] Brigades of Navarre, Italian support troops and an important air force of more than one hundred[n. 2] Heinkel He 51 and Fiat CR.

[13] For its part, the republican defense, led by General Francisco Llano de la Encomienda, had 150,000 men between the three provinces of Biscay, Cantabria and Asturias, with a notable mass of artillery (350 muzzles), a tank regiment and abundant ammunition and weapons.

[15] José Antonio Aguirre holds a war council with Gamir and the Soviet military advisor Vladimir Gorev and they agree to defend the Biscay's capital all costs.

[16] On the morning of June 19, 1937, the 1st and 4th Brigades advanced towards the estuary of Bilbao, while the 5th overflowed Mount Artxanda and descended through Begoña and Deusto over the Arenal [es].

It also represented a great moral and propaganda victory for the Requetés, who evoked the memory of General Tomás de Zumalacárregui, who died in the siege of the town a century earlier, during the First Carlist War.

[19] On September 5, 1937, the 1st Brigade of Navarre would form the advance guard of the Nationalists in the Asturias Offensive, clashing against fierce Republican resistance in the mountain pass of El Mazuco.

Rafael García Valiño Agustín Muñoz Grandes Miguel Abriat Cantó [es] Helí Rolando de Tella y Cantos