The Biscay Campaign () was an offensive of the Spanish Civil War which lasted from 31 March to 1 July 1937. 50,000 men of the Eusko Gudarostea met 65,000 men of the insurgent forces. After heavy combats the Nationalist forces with a crushing material superiority managed to occupy the city of Bilbao and the Biscay province. Background By late October 1936, all Gipuzkoa was occupied by the rightist rebel forces. The western front settled at the foot of Intxorta (Elgeta). However, Mola did not hide his plans to use air force against Basque territory loyal to the Republic. Despite Basque nationalist attempts at guaranteeing no shelling on civilians, Spanish Nationalist aircraft raided Bilbao on September 25 and 26, an indiscriminate attack on its starving population that spread a blaze of outrage across the city. Oblivious to foreseeable consequences, the Nationalists resumed ferocious air strikes against the city on 4 January 1937, prompting yet another outcry of indignation and an assault on the prison-ships where right-wingers were being held. It resulted in a death toll of 224. On 22 March 1937, Franco decided to halt his offensive against Madrid and start an offensive against the northern Republican held zone. The northern zone was politically divided and isolated from the central Republican zone. Furthermore, there was most of Spanish iron and coal and the chemical plants of Biscay. The Nationalists decided to start the occupation of the northern Republican zone with the conquest of the Biscay province. Opposing forces The Nationalists had the Emilio Mola's Army of the North (55,000 men). The Nationalist attack started with the Navarrese Division, led by the General José Solchaga. This division had four brigades led by the Colonels Garcia Valiño, Alonso Vega, Cayuela and Latorre (18,000 men) and the Black Arrow division (8,000 men with Italian officers). This force was established between Vergara and Villareal, on the border of the Biscay province. The Nationalist had also 200 guns, 120 aircraft, the battleship España, the cruisers Canarias and Almirante Cervera and the destroyer Velasco. Opposing them, the Republicans had General Francisco Llano de la Encomienda's Army of the North, theoretically numbered 150,000, but there were no unity between the Basque Nationalists, the Asturians and the Santaderinos. The Basque Army in Biscay had 30,000 men (most of them Basque Nationalists and also Asturians). The Republicans also had 140 guns, 25-30 aircraft, two destroyers and three submarines. The offensive