Could Germany invade Britain in 1940 with intact French, Italian and Soviet fleets plus completed planned ships?
Short answerSuch a fleet might change the balance under the question's impossible 1940 construction premise, but moving Mediterranean ships past Gibraltar remains a major obstacle.
NotesGiving Germany the intact French, Italian and Soviet fleets, together with their completed planned ships, would create an overwhelming force that might make Sea Lion possible. Completing those programmes on plausible schedules pushes the scenario toward 1944; their sudden availability in 1940 requires the question's imagined intervention. Even then, ships in the Mediterranean must get past Gibraltar before they can support the invasion. British submarines, mines, shore guns and surface forces could prevent the fleets from joining. Passing Gibraltar would still leave the problem of approaching the Channel through further defended waters.