In Italy, the Allies suffered a long stalemate at the German Gustav Line. In May 1944, three Goumier groupes, under the name Corps de Montagne, were the vanguard of the French Expeditionary Corps attack through the Aurunci Mountains during Operation Diadem, the fourth Battle of Monte Cassino. Here the Goums more than proved their value as light, highly mobile mountain troops who could penetrate the most vertical terrain in fighting order and with a minimum of logistical requirements. Most military analysts consider the Goumiers' manoeuvre as the critical victory that finally opened the way to Rome. Goumiers were armed by the US and wore early war US helmets and webbing but retained their traditional long brown woolen striped coats and carried fierce knives which they were adept in using.