The United States have never had the plants to kill Adolf Hitler. It is the Germans who had a lot of plots to kill Hitler, but none of them worked. The most plausible date for SOE's assassination of Hitler would have been around 13-14 July 1944. By this time the Russians had reached the old Polish-Soviet frontier.
I don't believe so but the British, Russians, and even Germans tried to kill him. Only Hitler was successful where 3 nations failed. One of the most famous attempts on his life was at the Wolfs Lair. On July 20th Nazi officer Claus Von Stauffenberg detonated a bomb which would have killed Hitler had the meeting not been moved to another building and had the bomb not been moved behind the tables legs. A second charge was supposed to be detonated but Stauffenberg had insufficient time to ready the second bomb.