The offensive in the Rhine river valley area started on 7 September, four days after France declared war on Germany. Since the "Wehrmacht" was occupied in the attack on Poland, the French soldiers enjoyed a decisive numerical advantage along their border with Germany. Eleven French divisions advanced along a line near Saarbrücken against weak German opposition. The attack did not result in the diversion of any German troops. The all-out assault was to have been carried out by roughly 40 divisions, including one armoured, three mechanised divisions, 78 artillery regiments and 40 tank battalions. The French Army had advanced to a depth of and captured about 20 villages evacuated by the German army, without any resistance. The half-hearted offensive was halted after France seized the Warndt Forest, of heavily mined German territory.