Immediately after the German occupation of France, Rundstedt, Blumentritt, and others were tasked with preparing for the invasion of Great Britain. This plan, as handed down from high command, was designated Operation Sea Lion. Blumentritt helped with the details of the plan, and several exercises were carried out in preparation for it, but he never believed that it was a serious option, or that Hitler intended to carry it out. He said that at the end of July or August "...Field-Marshal von Rundstedt was in Berlin, and Hitler stated quite clearly to him that he did not intend to carry out "Sea Lion"," and further, "By the end of September it was clear that the invasion of England was off."