Many of the leaders among the British and Americans thought that there was a significant chance that the D-Day landings could fail. There were estimates (not seriously thought out, AFAIK, but still) of 20% to 50% chance of failure. Even the most sanguine optimist had to acknowledge that sufficient bad weather at just the wrong time could override all the planning and preparation and resources the Allies put in.
So - if one were the Combined Chiefs of Staff, or Roosevelt and Churchill, what was the backup plan?
It would seem to me that given the non-trivial risk of failure, some thought should have been given to the question of what to do in that case. That is, what different strategic moves should the Allies make in that case? It would have been stupid to have all the other forces allocated to the OVERLORD campaign standing idle.
Did the Allied high command actually work on any such alternate plans?.
Please note that I am not asking for the suggestions or thoughts of anyone today - the members of this board. I ask if any of the very knowledgeable WW II buffs among the members knows what the Allies actually considered. This would be an obscure subject, as such plans, if there were any, would have gone into a file cabinet to be forgotten by D+4.
Does anyone know anything about this?