The Battle of Madrid in November 1936 had been fought to a standstill, with the Nationalists under Franco failing to take the city. They then started to besiege it, aiming to cut its links to the rest of Spain. Franco decided to attack the city from the north-west in order to cut off water and electricity supplies from the Sierra de Guadarrama and encircle the city. After a failed offensive in November, the Nationalists summoned a force of 17,000 men, led by General Orgaz, with four mobile brigades (led by Garcia Escamez, Barron, Saenz de Buruaga and Monasterio), backed by heavy artillery and Ju-52 bombers. The Republican army had a few battalions led by Luis Barceló.