Could the U.S. portion of D-Day invasion have been as large as Operation Downfall?

Question for the board. From what I've read of the proposals for Operation Downfall (the planned invasion of Japan), the forces earmarked for Downfall vastly exceeded the U.S. forces that took part in the D-Day invasion. Operation Downfall was to involve 42 aircraft carriers, 24 battleships, and 400 destroyers on the naval side. On the army side, 14 divisions were to take part in the initial landings, with 42 divisions to take part in Operation Coronet later. So my question is, could the U.S. have implemented as large or nearly as large a force for the Normandy invasion?

To answer my own question, I'm guessing an armada of 42 aircraft carriers and 24 battleships create severe logistical difficulties with being deployed in the English Channel, not to mention that such a fleet would not really be needed to cross the Channel to France, while it was probably necessary for the Japanese invasion. But what about the army divisions allocated for Operation Downfall? Is there a reason the U.S. couldn't or didn't contribute as many army divisions for D-Day as it planned to for Downfall? Was it that America was still fighting both Germany and Japan in 1944 and didn't have the forces available, whereas with Downfall the U.S. only had to worry about Japan? Those are just some guesses off the top of my head. Anyone know the answer to this?
 
I would guess that part of it has to do with the fact that the beaches of Normandy just aren't that big. With the international contingent as well, eventually you're just going to run out of places to put people.
 
If America didn't need to fight Imperial Japan at all...

Then any surplus building capacities would have been sent for the cross channel invasion ...

CVLs and CVEs would probably be more suitable for the English Channel than the Fleet Carriers that were Saratoga / Yorktown / Essex class that needed the sealanes of the Bay of Biscay or North Sea instead of the narrow straights of Dover for starters...

Tho convincing General Marshall to allow the Six US Marine Divisions to partake in the invasion of Normandy beach would be rough since there were some speculation that he wasn't too please with them during WW1 and regarded them as publicly hounds to garner recognization out of proportion of their actions during WW1 ...
 
I don't know if the U.S. expected the same amount of casualties in D-Day as in Operation Downfall. The U.S. expected 500,000 wounded and 500,000 dead after Operation Downfall. Japan probably had more troops available than Germany because they were only fighting the U.S. as opposed to Germany fighting on two fronts with the Eastern front taking everything they had
 

nbcman

Donor
Question for the board. From what I've read of the proposals for Operation Downfall (the planned invasion of Japan), the forces earmarked for Downfall vastly exceeded the U.S. forces that took part in the D-Day invasion. Operation Downfall was to involve 42 aircraft carriers, 24 battleships, and 400 destroyers on the naval side. On the army side, 14 divisions were to take part in the initial landings, with 42 divisions to take part in Operation Coronet later. So my question is, could the U.S. have implemented as large or nearly as large a force for the Normandy invasion?

To answer my own question, I'm guessing an armada of 42 aircraft carriers and 24 battleships create severe logistical difficulties with being deployed in the English Channel, not to mention that such a fleet would not really be needed to cross the Channel to France, while it was probably necessary for the Japanese invasion. But what about the army divisions allocated for Operation Downfall? Is there a reason the U.S. couldn't or didn't contribute as many army divisions for D-Day as it planned to for Downfall? Was it that America was still fighting both Germany and Japan in 1944 and didn't have the forces available, whereas with Downfall the U.S. only had to worry about Japan? Those are just some guesses off the top of my head. Anyone know the answer to this?

The US didn't have enough amphibious assault vessels in mid-1944 to land 14 divisions at once. They had to delay Overlord by a month to get enough landing craft to invade with 5 divisions divided between the US, the UK and Canadian forces. To get enough landing craft to land 14 divisions, it would take stripping all landing craft from the Mediterranean and Pacific theaters plus months more production at OTL rates to get enough landing craft for 14 US divisions plus 3 UK/Canadian divisions. But there was not sufficient space on the beaches of Normandy to deploy that many divisions.
 
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CalBear

Moderator
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Monthly Donor
There was no need for any carriers (or for 400 destroyers for that matter). That was the nice thing about having a significant land mass 100 miles away. The Downfall force was going to have to cart everything it needed across the Pacific, from as far away as the Marshall Islands, and defend against what the U.S. expected to be up to 10,000 kamikaze aircraft, plus suicide boats. That sort of threat wasn't present at Normandy. While there is no such thing as too much naval gunfire support 24 battleships would be sort of short on elbow room in the Channel once thousands of landing vessels, escorts, transports and the like were in the mix.

14 divisions would require two full waves of landings, unless the landing zone was massively increased.
 

TFSmith121

Banned
It's worth noting that the Allied forces afloat and combat

Question for the board. From what I've read of the proposals for Operation Downfall (the planned invasion of Japan), the forces earmarked for Downfall vastly exceeded the U.S. forces that took part in the D-Day invasion. Operation Downfall was to involve 42 aircraft carriers, 24 battleships, and 400 destroyers on the naval side. On the army side, 14 divisions were to take part in the initial landings, with 42 divisions to take part in Operation Coronet later. So my question is, could the U.S. have implemented as large or nearly as large a force for the Normandy invasion?

To answer my own question, I'm guessing an armada of 42 aircraft carriers and 24 battleships create severe logistical difficulties with being deployed in the English Channel, not to mention that such a fleet would not really be needed to cross the Channel to France, while it was probably necessary for the Japanese invasion. But what about the army divisions allocated for Operation Downfall? Is there a reason the U.S. couldn't or didn't contribute as many army divisions for D-Day as it planned to for Downfall? Was it that America was still fighting both Germany and Japan in 1944 and didn't have the forces available, whereas with Downfall the U.S. only had to worry about Japan? Those are just some guesses off the top of my head. Anyone know the answer to this?

It's worth noting that the Allied forces afloat and combat-loaded for OVERLORD amounted to six reinforced infantry divisions, three US (1st, 4th, 29th), two British (3rd and 50th) and one Canadian (3rd); at almost the same time, the US had the equivalent of five divisions afloat simultaneously for the Marianas (2nd, 3rd, 4th Marine divisions; 27th Infantry Division; and the 1st Marine Brigade (square, and reinforced)) as well as the 41st Division (Reinforced) for Biak.

Add that all together, and one gets to 12 divisions, pretty easily. The Allies could have done OVERLORD and (for example) an operation the size of ANVIL (3 division equivalents in the assault, 3 afloat for the follow-up) simultaneously, absent the needs of the Pacific.

Best,
 
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