What if the Royal Navy upgraded Sea Vixen to an F3 standard instead of buying the Phantom?
Short answerThe upgrade would demand major structural and propulsion changes yet still leave an older, less capable aircraft; buying the Phantom remained the stronger carrier-defense choice.
NotesA Sea Vixen F3 is rejected as a poor substitute for the Phantom, particularly the Rolls-Royce-powered version. The name F3 does not settle the scope of the proposed upgrade: the discussion distinguishes a subsonic modernisation for early AIM-9 missiles from a much more extensive supersonic conversion. Sea Vixen's design belongs to an earlier period, and aviation changed substantially between its early development and retirement. The supersonic proposal would require stronger wing spars and fuel tanks, changes to the pressurisation system, and new engines. That amount of reconstruction weakens the case that retaining Sea Vixen would save enough money to justify its lower capability.