The German Ardennes offensive in mid-December forced the division to withdraw to defensive positions near Elsenborn Ridge, where the German drive was halted. When the initial thrusts of a full-scale German counter offensive threatened the right flank of his division, Robertson, fully aware of the urgency of the situation, personally assumed command of the defense of a vital road junction to delay the enemy long enough for his troops to take up defensive positions. Within an hour the first hostile tanks appeared 600 yards away and were immediately taken under fire on Robertson's orders.