In December 1975 most 5th Brigade units were committed to the border areas of Tucumán with over 5,000 troops deployed in the province. There was however, nothing to prevent infiltrating through this outer ring and the ERP were still strong inside Buenos Aires. Mario Santucho's Christmas offensive opened on 23 December 1975. The operation was dramatic in its impact, with ERP units, supported by "Montoneros", mounting a large scale assault against the army supply base "Domingo Viejobueno" at the industrial suburb of Monte Chingolo, south of Buenos Aires. The attackers were defeated and driven off with 53 ERP guerrillas and 9 supporting militants killed. Seven army troops and three policemen were reported killed. In this particular battle the ERP and supporting Montoneros militants had about 1,000 deployed against 1,000 government forces. This large-scale operation was made possible not only by the planning of the guerrillas involved, but also by their supporters who provided houses to hide them, supplies and the means of escape.