The Iron Ring, Bilbao

This postcard, part of a series issued after the war, shows a machine gun nest that was part of the imposing Iron Belt of Fortifications that defended Bilbao.

The Francoist conquest of Guipúzcoa in October 1936, left the northern part of Republican Spain isolated from France and in a precarious position. From then on, it was supplied by sea, but the bulk of the Francoist fleet was concentrated in the Cantabrian Sea, which made it dangerous for Republican merchant shipping. The Republican fleet was concentrated in the Mediterranean where, harassed by the Italians and Germans, the weapons and fuel essential for the war effort arrived.

On March 31, 1937, General Emilio Mola sent his armies to take the northern front, starting with Vizcaya. They had more men and more equipment than the Republicans, who were also divided into three autonomous political units: the Basque Country, Asturias, and Santander, each with its own militias and little cooperation among them. Moreover, these forces had not evolved at the same pace as the regular army in the rest of the Republican zone. Even so, a campaign Mola expected to be over in a few weeks lasted seven months. There were two main reasons for this: the mountainous terrain and staunch Republican resistance.

The forces defending Vizcaya were made up primarily of 27 Basque nationalist battalions, 8 Socialist ones, and 11 assorted others. The Republic did everything possible to send military equipment north, including planes that flew over enemy territory, but the attackers, who included Italians and Carlist militias, enjoyed a clear superiority in arms and materiel. The unexpectedly stiff Basque resistance, assisted by Republican offensives in Segovia and Huesca, led the Francoists to take extreme measures to terrorize the population. The most famous was the bombing of Guernica in which 300 people were killed. The breaching of the famous Iron Belt fortifications that surrounded Bilbao on June 13 made possible when the engineer Alejandro Goicoechea delivered the plans to the enemy, sealed Vizcaya’s fate. The city fell on June 19. The decision of the Basque government not to destroy the region’s important heavy industry meant that the rebels inherited it intact.

The Basque army retreated to Santander, accompanied by 200,000 refugees who were attacked by rebel planes. The Republic tried to shore up the northern front by launching an attack at Brunete, near Madrid, that delayed the Francoist advance for a few weeks. For many Basques, who had never been whole-hearted supporters of the Republican project, the fall of Vizcaya meant that their war was over. Secret negotiations between Basque nationalist and Italian authorities would begin shortly after. Over the next two months, this separate peace would have grave implications for the defence of Santander.