How would today's Royal Navy be used if it appeared in the First or Second World War?
Short answerIts submarines and carrier aircraft would dominate because period forces could neither find nor effectively engage them.
NotesAn Astute-class submarine could operate off Germany with no period anti-submarine system able to contain it. Queen Elizabeth-class carriers and F-35Bs could strike European targets while remaining effectively invisible and unreachable to contemporary defenses. The result depends less on the modern fleet's small hull count than on an eighty-year gap in sensing, weapons, and propulsion. The closest comparison is taking HMS Warrior to Trafalgar, where one ship's technology invalidates the opponent's normal tactics.