The invasion of Sicily began on 9 July and was successfully completed by 17 August. Churchill was then all for driving straight up the Italian mainland with Rome as the main target, but the Americans wanted to withdraw several divisions to England in the build-up of forces for Operation Overlord, now scheduled for the spring of 1944. Churchill was still not keen on "Overlord" as he feared that an Anglo-American army in France might not be a match for the fighting efficiency of the Wehrmacht. He preferred peripheral operations, including a plan called Operation Jupiter for an invasion of northern Norway. Events in Sicily had an unexpected impact in Italy. King Victor Emmanuel sacked Mussolini on 25 July and appointed Marshal Badoglio as Prime Minister. Badoglio opened negotiations with the Allies which resulted in the Armistice of Cassibile on 3 September. In response, the Germans activated Operation Achse and took control of most of Italy. Although he still preferred Italy to Normandy as the Allies' main route into the Third Reich, Churchill was deeply concerned about the strong German resistance at Salerno and, later, after the Allies successfully gained their bridgehead at Anzio but still failed to break the stalemate, he caustically said that instead of "hurling a wildcat onto the shore", the Allied force had become a "stranded whale". The big obstacle was Monte Cassino and it was not until mid-May 1944 when it was finally overcome, enabling the Allies to at last advance on Rome, which was taken on 4 June.