US reaction if Japan attacks British colonies+DEI, but not US

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jahenders

Banned
What if the Japanese opted to gamble and attack the British and Dutch in 1941 without going after the Philippines and US holdings? I'd imagine they could attack earlier than IOTL and keep forces in reserve just in case the US opted to intervene. What would happen then if the US was left out of the Japanese offensives? How would the British react? Would the US public be interested in war?

While it would obviously take a different Japanese calculation, I think this would be a viable option. Japan would just have to conclude that the risk (probability * impact) of US involvement if the Japanese don't attack the US is lower than the risk (100% probability * risk) of getting the US involved by attacking PI/Pearl.

If Japan had attack UK/Dutch holding and not the US, the US would definitely up the rhetoric, embargoes, Lend Lease, etc. However, public sentiment for the US to get into a war for the British Empire still wasn't there.

Chances are the US would find a causus belli within 6 months (i.e. by Jun of 42), but it would almost certainly be with Germany. Assuming that's the case, it might be hard to justify the declaration of war including Japan if it scrupulously avoided attacks on US holdings. Even if Japan is included, the argument for Germany-first is going to be MUCH stronger, so the Pacific might be largely a backwater with the US on defense until 43.

So, if the Japan doesn't attack the US:
- The US likely won't enter the war until 3-6 months later and with an even stronger European focus
- Torch probably won't be until early 43
- Sicily is later in 43
- Probably no Coral Sea or Midway in 42

In general, had Japan not attacked the US, it might have set US involvement in the war back 3-6 months in Europe and possibly 6-12 in the Pacific.
 

Deleted member 1487

While it would obviously take a different Japanese calculation, I think this would be a viable option. Japan would just have to conclude that the risk (probability * impact) of US involvement if the Japanese don't attack the US is lower than the risk (100% probability * risk) of getting the US involved by attacking PI/Pearl.

If Japan had attack UK/Dutch holding and not the US, the US would definitely up the rhetoric, embargoes, Lend Lease, etc. However, public sentiment for the US to get into a war for the British Empire still wasn't there.

Chances are the US would find a causus belli within 6 months (i.e. by Jun of 42), but it would almost certainly be with Germany. Assuming that's the case, it might be hard to justify the declaration of war including Japan if it scrupulously avoided attacks on US holdings. Even if Japan is included, the argument for Germany-first is going to be MUCH stronger, so the Pacific might be largely a backwater with the US on defense until 43.

So, if the Japan doesn't attack the US:
- The US likely won't enter the war until 3-6 months later and with an even stronger European focus
- Torch probably won't be until early 43
- Sicily is later in 43
- Probably no Coral Sea or Midway in 42

In general, had Japan not attacked the US, it might have set US involvement in the war back 3-6 months in Europe and possibly 6-12 in the Pacific.
The only problem is the Axis pact requires Japan and Italy to DoW the US if the US DoWs Germany. The pact was specifically aimed at the US. If that is the case then the US has to be prepared for Japanese reaction, which would probably cause a fair bit of political fallout if things go badly for the US initially.
 
lets consider a possible bad outcome for Japan

Somehow the UK prepares a bit, and performs somewhat better than historically.

Japan wins but loses a a battleship, a carrier and some cruisers, as well as a number of transport ships. Furthermore several more battleships face six months in dry dock. Japanese military performance is good, but its strengths and weaknesses are clear for the US to see. The biggest problem for now facing Japan is probably a shortage of shipping, made slightly worse from modest losses to submarines.

After three months Singapore and other key locations fall, Japan now has an extensive empire to support and protect, and a large US force on its supply line as the phillipines is heavily reinforced.

Suddenly the balance of power versus the US looks less good. The US is hurriedly upgrading its ships, and adjusting tactics, it is laying down a large fleet and making demands that will lead to war.

Fighting in Burma is ongoing, but the difficulty in supplying troops there is proving problematic and limits the numbers that can be put in the field.

Suddenly Japan finds itself at war, US submarines based out of Manila hit supply convoys, and the US airforce prevents a swift assault on the Phillipines, and when it does happen the beachhead turns into a quagmire as US light tanks
Formations inflicts heavy losses on the lightly equipped Japanese forces.

I think this plausible scenario makes it very tough for Japanese planners leave the US out of the war from day one. I think Japan could be left worse off by not going for the US on day one.
 

Deleted member 1487

lets consider a possible bad outcome for Japan

Somehow the UK prepares a bit, and performs somewhat better than historically.

Japan wins but loses a a battleship, a carrier and some cruisers, as well as a number of transport ships. Furthermore several more battleships face six months in dry dock. Japanese military performance is good, but its strengths and weaknesses are clear for the US to see. The biggest problem for now facing Japan is probably a shortage of shipping, made slightly worse from modest losses to submarines.

After three months Singapore and other key locations fall, Japan now has an extensive empire to support and protect, and a large US force on its supply line as the phillipines is heavily reinforced.

Suddenly the balance of power versus the US looks less good. The US is hurriedly upgrading its ships, and adjusting tactics, it is laying down a large fleet and making demands that will lead to war.

Fighting in Burma is ongoing, but the difficulty in supplying troops there is proving problematic and limits the numbers that can be put in the field.

Suddenly Japan finds itself at war, US submarines based out of Manila hit supply convoys, and the US airforce prevents a swift assault on the Phillipines, and when it does happen the beachhead turns into a quagmire as US light tanks
Formations inflicts heavy losses on the lightly equipped Japanese forces.

I think this plausible scenario makes it very tough for Japanese planners leave the US out of the war from day one. I think Japan could be left worse off by not going for the US on day one.

That's basically a close to worst possible case for the Japanese.
 

jahenders

Banned
The only problem is the Axis pact requires Japan and Italy to DoW the US if the US DoWs Germany. The pact was specifically aimed at the US. If that is the case then the US has to be prepared for Japanese reaction, which would probably cause a fair bit of political fallout if things go badly for the US initially.

Granted. One way or another, the US would wind up at war with Japan once it goes to war with Germany.

My two main points are:
- If Japan doesn't attack, US entry is delayed 3-6 months
- If Japan doesn't attack, the US' Germany-first focus is even stronger than IOTL so the Pacific gets less resources, further delaying US efforts there.
 
That's basically a close to worst possible case for the Japanese.

Bad certainly! But worse would be Britain have tanks and stronger leadership in Malaya. I find the Japanese dilemma fascinating. Assuming they wanted war they had remarkably few choices about how to go about it.
 

Deleted member 1487

Granted. One way or another, the US would wind up at war with Japan once it goes to war with Germany.

My two main points are:
- If Japan doesn't attack, US entry is delayed 3-6 months
- If Japan doesn't attack, the US' Germany-first focus is even stronger than IOTL so the Pacific gets less resources, further delaying US efforts there.
Agreed, unless the US opts to get more aggressive in response to Japanese aggression and the Brits beg for US help in the Pacific to stabilize that situation. If the Japanese then declare war and move on US positions in the Pacific, does the US strip out assets from the Atlantic as per OTL to try and cover the East? I mean the Japanese have the greatest ability to threaten the US and its positions with its navy, Germany has little to no ability to threaten the US and its holdings.
 
Is this before any invasion of USSR?

recall they would only gamble on Vichy Indochina before Germans-Soviets started death match.

maybe they move only on DEI? although that might be distinction without a difference?

how would British react to that ? did they have committed joint defense plan for DEI?

Is it even feasible for Japan to just try for DEI? (in addition to at least some presence in Vichy-controled Indochina)

under the theory or premise that the puppet regimes in place are allowing the occupation.
 
If the Japanese then declare war and move on US positions in the Pacific, does the US strip out assets from the Atlantic as per OTL to try and cover the East?

US war plans for the Pacific long before 1941, or even 1939, generally called for the abandonment of the western Pacific holdings until the relevant combat and logistical bases can be built to support a US drive towards Japan. By the time the US is ready to enter the war, it won't need to strip out assets from the Altantic in order to cover the east any more then it did so OTL.

I mean the Japanese have the greatest ability to threaten the US and its positions with its navy, Germany has little to no ability to threaten the US and its holdings.

Japan is in just as bad a position to threaten the US and its position as Germany or the Soviet Union in final analysis.
 
The US would have slapped Japan with even more crushing economic restrictions and moved to increase its already not-insubstantial 'informal' commitment against her, more or less to the point where America would become a belligerent within a few months' to maybe a year's time.
 
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