and Stalin's suspicions allayed". However some source material contradicts the official reported accord between Churchill and Roosevelt, claiming that Churchill did not fully subscribe to the doctrine of "unconditional surrender". The New York Times correspondent Drew Middleton, who was in Casablanca at the conference, later revealed in his book, Retreat From Victory, that Churchill had been "startled by the [public] announcement [of unconditional surrender]. I tried to hide my surprise. But I was his [Roosevelt's] ardent lieutenant". According to former U.S. ambassador to the Soviet Union Charles Bohlen, "Responsibility for this unconditional surrender doctrine rests almost exclusively with President Roosevelt". He guessed that Roosevelt made the announcement "to keep Soviet forces engaged with Germany on the Russian front, thus depleting German munitions and troops" and also "to prevent Stalin from negotiating a separate peace with the Nazi regime". That the war would be fought by the Allies until the total annihilation of enemy forces was not universally welcomed. Diplomatic insiders were critical that such a stance was too unequivocal and inflexible, would prevent any opportunity for political maneuvering and would be morally debilitating to French and German resistance groups. The British felt that arriving at some accommodation with Germany would allow the German Army to help fight off a Soviet takeover of Eastern Europe. To Churchill and the other Allied leaders, the real obstacle to realising that mutual strategy with Germany was the leadership of Adolf Hitler. Allen Dulles, the chief of OSS intelligence in Bern, Switzerland, maintained that the Casablanca Declaration was "merely a piece of paper to be scrapped without further ado if Germany would sue for peace. Hitler had to go". There is evidence that German resistance forces, highly placed anti-Nazi government officials, were working with British intelligence, MI6, to eliminate Hitler and negotiate a peace with the Allies. One such man was Admiral Wilhelm Canaris, head of German intelligence, the Abwehr. His persistent overtures for support from the United States were ignored by Roosevelt. Topics of discussion and agreements European invasion Roosevelt, with advice from General George C. Marshall, the U.S. Army Chief of Staff, lobbied for a cross-Channel invasion of Europe. Churchill, with advice from the British Chiefs of Staff, led by General Sir Alan Brooke, the Chief of the Imperial General Staff (CIGS, the professional head of the British Army), felt the time was not opportune, and favored an Allied assault on the island