On August 13, Mola met Franco in Seville and decided to capture San Sebastián and Irún in order to cut the Basques off from the French Border at the western end of the Pyrenees.

[3][4] The campaign was initially conceived by General Emilio Mola as an advance to Irún, to cut the northern provinces off from France, and to link up with the Nationalist garrison in San Sebastián that was to have seized that city.

[5] Following the failure to relieve the siege of the Nationalists in San Sebastian, the forces of Beorlegui resumed their advance on Irún to cut off the northern provinces of Gipuzkoa, Biscay, Santander and Asturias, from their source of arms and support in France by taking that city.

[7] On August 17, the rebel battleship España, the cruiser Almirante Cervera and the destroyer Velasco arrived at San Sebastián and started to shell the city.

After that, German Ju 52 bombers and other Italian planes bombarded on a daily basis the bordering towns of Hondarribia and Irun,[1] as well as San Sebastián.

The poorly armed and untrained leftist and Basque nationalist militias fought bravely but could not fend off the rebel push, in no small part due to an inability to get ammunition to the defending forces.

There, the resistance of the Basque pro-republican forces, backed up with 8,000 rifles smuggled in extremis by Lezo Urreiztieta to Santander on 24 September,[14] along with the exhaustion of the Nationalists, resulted in an end of the offensive until the War in the North began.

[17] On occupation during September, a Comisión Gestora or Management Commission was appointed by the rebel nationalists comprising the factions involved in the military insurrection, i.e. Carlists, Falangists, and others.

[20] The hatred underlying the crackdown was evidenced by the assassination of José Ariztimuño 'Aitzol', a priest and major personality of the Basque cultural renaissance during the previous years), tortured and shot on 18 October in the Hernani cemetery, along with other ecclesiastic and civilian victims found fleeing.