On February 7, after having armed all its battalions, it was initially located in Madrid as a reserve to intervene in the Battle of Jarama. Attached to the 11th Division of Enrique Líster, the 70th MB took part in the fighting that developed around Pingarrón, between February 19 and 22; the unit lost half of its troops during these days, without being able to conquer the disputed position. Moved to the rear, it underwent a reorganization.