Franco’s plans for the Basque campaign of March-June 1937 grew out of the realization that Madrid could not be immediately taken, and the war won quickly. Many thought the Basque citadel of Bilbao could be taken within weeks of the start of operations. A ‘ring of iron’ was the main defense line of Bilbao and was counted on by the Basques to hold off any Nationalist attack. The ring of iron consisted of two lines about 200-300 yards apart, lacking depth and protection, standing on hills without camouflage. The Nationalist offensive began on March 31st but dragged on for months while the advance ground inexorably forward. By early June the final ring around Bilbao had been reached. The Navarrese 5th Brigade was hurled at what was thought to be a weak spot in the Basque line.
