Possible Clues:

• Code name for the 51-Down operation
• Supremo for D-Day operation?
• Wartime operation ended by Kitchener, perhaps
• Supreme leader – D-day operation
• Codename for the Allied operation to invade Normandy which began on D-Day in 1944
• Supreme ruler
• Operation name for the Second World War invasion of Normandy
• Too much work? Right for a ruler
• Drool dodderingly about clergyman turning up in wartime operation
• Ruler's operation in wartime