Jim, you are correct. On December 24, 1943, Ike was appointed supreme commander of the Allied Expeditionary Force, and the next month he was in London making preparations for the massive thrust into Europe. Monty worked closely with U.S. General Dwight Eisenhower planning and implementing the D-Day invasion of France. In September 1944, he was made a field marshal -- the highest rank in the British Army.
After the Invasion of Sicily, Montgomery returned to Britain to take command of the 21st Army Group which consisted of all Allied ground forces that would take part in Operation Overlord, the invasion of Normandy. Preliminary planning for the invasion had been taking place for two years, most recently by COSSAC staff (Chief of Staff to the Supreme Allied Commander). Montgomery quickly concluded that the COSSAC plan was too limited, and strongly advocated expanding the plan from a three-division to a five-division assault. As with his takeover of the Eighth Army, Montgomery travelled frequently to his units, raising morale and ensuring training was progressing. On 7 April and 15 May he presented his strategy for the invasion at St Paul's School. He envisaged a ninety day battle, ending when all the forces reached the Seine, pivoting on an Allied-held Caen, with British and Canadian armies forming a shoulder and the U.S. armies wheeling on the right.
Montgomery was in command of the Allied land forces, but was not the Supreme Commander.
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"