WI: US with Pacific War only?

So, what if say, Hitler for whatever reason decides not to declare war on the US after PH?
And US now has a war with Japan as in OTL?

When could the US defeat Japan? What capabilities, especially US Army and Army Air Force, need to do that? In comparison with the OTL... What about Project Manhattan?
 
In comparison with the OTL... What about Project Manhattan?

December 6, 1941
Vannevar Bush holds a meeting in Washington to organize an accelerated research project. Arthur H. Compton remains in charge. Harold Urey is appointed to develop gaseous diffusion and heavy water production at Manhattan, NY; Ernest O. Lawrence will investigate electromagnetic separation at the University of California at Berkeley; and Eger Murphree will develop centrifuge separation and oversee engineering issues. James B. Conant advocates pursuing Pu-239, but no decision on this is made.
 
So, what if say, Hitler for whatever reason decides not to declare war on the US after PH?
And US now has a war with Japan as in OTL?

When could the US defeat Japan? What capabilities, especially US Army and Army Air Force, need to do that? In comparison with the OTL... What about Project Manhattan?

Getting to effective air bombing range and blockade range of Japan requires either building the Essex class carriers & fleet train for a direct cross Pacific campaign, or shipping the wherewithal all the long way around to China. Either takes several years to accomplish. Perhaps some months can be shaved off but getting to Japans throat could not be done with the large land army used in Europe.
 
Full concentration on assisting China, providing the National Revolutionary Army with advisors and supplying the Chinese. There should be a lot more American military personnel in China. If done right, it's likely the ROC emerges from WW2 a lot stronger.

The Navy will bear some of the heaviest fighting, while the US will outnumber Japan's forces quickly once they get their conscription going. The USAAF would be likely stationed in China and Burma as in OTL, plus the Marianas for firebombing Japan later on.

The British and Free French will still obtain their lend-lease, due to their Pacific colonies being attacked and taken by Japan.

On the downside, the Soviets will have to struggle for quite a long while without all that lend-lease.
 
Getting to effective air bombing range and blockade range of Japan requires either building the Essex class carriers & fleet train for a direct cross Pacific campaign, or shipping the wherewithal all the long way around to China. Either takes several years to accomplish. Perhaps some months can be shaved off but getting to Japans throat could not be done with the large land army used in Europe.

XB-36 mockup was ready in Sand Diego in 1942, but was set to low priority and moved to Fort Worth so B-24s could be built.

US may decide that bombing Japan from the West Coast or Alaska with a very long superheavy bomber might be of more use, without 'Germany First'
 
So, what if say, Hitler for whatever reason decides not to declare war on the US after PH?
And US now has a war with Japan as in OTL?

When could the US defeat Japan? What capabilities, especially US Army and Army Air Force, need to do that? In comparison with the OTL... What about Project Manhattan?

1. When the torpedo problem is solved.
2. When the submarine force is built, trained and capable.
3. When the amphibious assault forces are created.
4. When the strategic bomber force is created.
5. When the battle fleet is created, trained and capable.
6. When the central and southwest Pacific campaigns are conducted to completion.
7. When it all comes together to clamp down the blockade and strategic bombardments.

Four years to do all of this. Victory in late 1944 early 1945. It is not just % of industrial production, but time to create the tools and to mount the operations to come within range of the home islands.
 
With more shipping, aircraft and manpower available, I wonder if CBI gets more importance. There will be much more aircraft to carry cargo over the Hump, and land operations in Burma can be carried out more vigorously with more shipping and air transportation available. Thus the trickle given to ROC will increase to a flood and 14th AF will increase in importance. This can get the US within bombing range of Japan faster than the trans-pacific campaign which requires build-up of the USN carrier fleet and fleet train.
 
The US will also have far more material to test out and spare in the island-hopping that is to ensue, and you can expect to see plenty of US forces fighting in Burma.

In the long run, we'll see a lot of friendships built, as in OTL:

Friendship.jpg
 
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With more shipping, aircraft and manpower available, I wonder if CBI gets more importance. There will be much more aircraft to carry cargo over the Hump, and land operations in Burma can be carried out more vigorously with more shipping and air transportation available. Thus the trickle given to ROC will increase to a flood and 14th AF will increase in importance. This can get the US within bombing range of Japan faster than the trans-pacific campaign which requires build-up of the USN carrier fleet and fleet train.

Based on Kuomintang corruption and the horrible time, terrain, weather and movement impedence factors, the chances of RoC doing much more or of any US forces involved accomplishing much through the CBI more than was RTL done amounts so close to zero chance as to be frustrating in the throwing of good logistics down that rathole. Better to drive across the Pacific with the logistics wasted in the CBI and let the RoC act as it RTL did, as a huge sponge to absorb Japanese attention and resources.
 
Based on Kuomintang corruption and the horrible time, terrain, weather and movement impedence factors, the chances of RoC doing much more or of any US forces involved accomplishing much through the CBI more than was RTL done amounts so close to zero chance as to be frustrating in the throwing of good logistics down that rathole. Better to drive across the Pacific with the logistics wasted in the CBI and let the RoC act as it RTL did, as a huge sponge to absorb Japanese attention and resources.

Like I said earlier, it all depends if the KMT is able to rid itself of corruption and at least do something about its other problems to actually do well. The island hopping should be the main focus of the US here - how are they going to get to China easily if they can't cross the Pacific? Plus, you can't just let the IJN roam unchecked.
 
Based on Kuomintang corruption and the horrible time, terrain, weather and movement impedence factors, the chances of RoC doing much more or of any US forces involved accomplishing much through the CBI more than was RTL done amounts so close to zero chance as to be frustrating in the throwing of good logistics down that rathole. Better to drive across the Pacific with the logistics wasted in the CBI and let the RoC act as it RTL did, as a huge sponge to absorb Japanese attention and resources.

Striking through China is possible while USN will have to built up. In OTL the effort to help ROC forces was fairly minimal - in WWII standards. ITTL, there can be a load of US troops on resources spent not only in China, but in Burma and Indochinese theater as well, rolling through Thailand. Vietnam, Malaysia...

Like I said earlier, it all depends if the KMT is able to rid itself of corruption and at least do something about its other problems to actually do well. The island hopping should be the main focus of the US here - how are they going to get to China easily if they can't cross the Pacific? Plus, you can't just let the IJN roam unchecked.

It takes more time to build an effective USN striking machine - to mid 1944 - than to build the logistic chain to help CBI-campaign which can be done via shipping to India.
 
How are you getting equipment into China? Again, build up is the problem. Your options are basically a mud track owned by a foreign power.
 
How are you getting equipment into China? Again, build up is the problem. Your options are basically a mud track owned by a foreign power.

10 000 C-47's, 3000 C-46's and all the other transport planes which have less tasks due to no ETO or MTO. Ledo road will also presumably get more importance, as well as reconquest of Burma to open the Burma road again.
 
How are you getting equipment into China?
Simple FDR will order it shipped via the two best routes,
1- Via US East coast to Glasgow then onto Murmansk and along the TSR to Northern China...
2- Via US East coast to Gibraltar, Malta, Suez and on into Burma etc.....

I cant guarantee that everything will get to the end delivery destination of mainland China and inevitably the USN might get involved in defending the convoys from disguised Japanese forces trying to hide under false flags of the other Axis members....
 
Victory is assured by late 44 at worst IMO. However the war isn't going to end until either an invasion of the home islands or Los Alamos gets the bombs up and running.
 
So, if Japan is put in Potsdam-like situation in say september 1944, and with Manhattan fruits coming in about 9 months, what would the US do? Invasion? Bombing/blockade and then invasion? Bombing and blockade until they surrender?
 
There are two scenarios that can produce this situation.

One scenario is that the USA and Germany do not go to war after Pearl Harbor because the two countries are allies. You get FDR out of the picture and a fascist sympathetic government in Washington. Or Hitler is able to come to terms with Britain. Or the Nazis declare victory after the fall of France, don't occupy northern France, don't bomb the UK, attack British shipping, or help the Italians so eventually Churchill is replaced, the British come to terms, and there is no need for lend lease, and then after Pearl Harbor Germany declares was on Japan, though I don't see why the Japanese do the Pearl Harbor attack in this situation, it probably completely changes the Japanese strategy.

The second scenario is that Germany just does not declare war on the USA after Pearl Harbor.

The second scenario has been debated in this board, and there is strong evidence that the USA was shortly going to declare war on Germany anyway. German inaction may not be enough, though their declaring war on Japan would at least confusing things.

Some version of the first scenario involves multiple unpredictable changes in the world situation.

With a straight up war between the US and Japan, the US army is not that useful in an island-naval war, and with only air supply to Nationalist China possible there ithey can't send much there, even assuming Chiang would make good use of any additional material. And the Americans will always keep a fleet in the Atlantic regardless and in the actual war they didn
t have a problem with transferring assets to the Pacific as needed. Really nothing changes.

Despite Roosevelt's publically stated "Germany first" policy, if you look at exactly where Washington directed its forces, particularly transports, it really was "Japan first" through 1943.
 
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