The Wehrmacht was successfully able to delay the American advance towards the Rur. The Rur River line, whose holding was deemed necessary for the successful implementation of the Ardennes Offensive, was held. The preparation of the final Ardennes Offensive was mostly successful with Germany being able to build up enough troops in secrecy for a sufficient blow. On 16 December the Allies were taken by complete surprise and the Germans were quickly able to achieve a breakthrough. Later (14 until 26 January 1945), the Roer triangle was cleared during Operation Blackcock and only in February 1945 were the Allies finally able to cross the Rur, by then the road to the Rhine was clear.