Ace of aces is a title accorded to the top active ace within a branch of service in a nation's military in time of war. The title is most closely associated with fighter aces, though there are other types, such as tank aces and submarine aces.
Ace of aces is a title accorded to the top flying ace/fighter ace of a nation's air force during time of war.
Ace of the Deep is a title accorded to the top subsea ace/undersea ace/submarine ace of a nation's submarine force during time of war.