How would the Second World War change if practical jets and helicopters arrived early?
Short answerMerchant ships could become helicopter anti-submarine carriers quickly, making surfaced U-boat operations far more dangerous and possibly accelerating German development of Type XXI submarines.
NotesA helicopter needs a flight deck and hangar but not the full-length deck demanded by fixed-wing aircraft, so merchant conversions could be completed faster and on more hulls. Convoy helicopters would make surfaced submarine operations much more dangerous. Germany might respond by reducing investment in an unsuccessful U-boat campaign or by pursuing Type XXI-style boats earlier, while Allied access to wider resources would favor mass production and deployment.