On 25 July, the American First Army began Operation Cobra, which after the first two days, broke through the German defences south of St Lo. By the end of the third day of the operation, American forces had advanced south of the Cobra start line at several points. On 30 July, US forces captured Avranches, at the base of the Cotentin peninsula. The German left flank had collapsed and within 24 hours, units of the US Third Army entered Brittany and advanced south and west through open country, almost without opposition. The 1st SS, 9th SS and 116th Panzer divisions were shifted westward from Verrières Ridge to face this new threat.