The decision taken at Tehran was a final indication of American determination to stage the cross-Channel invasion and a defeat for Alan Brooke, Churchill's chief of staff and the principal opponent of premature action. Yet despite Brooke's procrastination, the British had in fact been proceeding with structural plans, coordinated by Lieutenant General Frederick Morgan, who had been appointed COSSAC (chief of staff to the supreme Allied commander [designate]) at the Anglo-American Casablanca conference in January 1943. His staff's first plan for Operation "Overlord" (as the invasion was henceforth to be known) was for a landing in Normandy between Caen and the Cotentin Peninsula in a strength of three divisions, with two brigades to be air-dropped. Another 11 divisions were to be landed within the first two weeks through two artificial harbours that would be towed across the Channel. Once a foothold had been established, a force of a hundred divisions, the majority shipped directly from the United States, were to be assembled in France for a final assault on Germany. In January 1944 Eisenhower became supreme Allied commander, and the COSSAC staff was redesignated SHAEF (Supreme Headquarters Allied Expeditionary Force).