Once again, either the Japanese destroy the west coast and butcher millions of Americans, or FDR scorches the west coast and uses human waves of patriots to stop the invasion. I already considered this possibility. This would have the same end effect. These patriots weren’t even a trained militia like we had in the Revolution. Who is going to feed them? They would end up diseased and useless. If they just drove to California or hopped on a train, then they would clog the very transport lines that the Army must use to get supplies to the 1.4 million soldiers. If you can’t explain how the actual Army would credibly stop the Japanese, then how should someone believe that a patriotic rabble would do it?

The Japanese have 4 million tons of shipping to keep their invasion force supplied. As CBR inadvertently pointed out in considerable detail, that is more than enough to sealift the invasion force along with two months supply and then continue to supply it. The USN subs are armed with dud torpedoes, so what is going to attack these ships, the USN carriers? The USN did not have surface raiders and the carriers would not have been risked. Remember, a damaged carrier must go to the east coast for repair or set in San Diego as a target. So how are the Japanese supply lines vulnerable?

The IJN does not have to send its forces to Panama or the southern tip of South America, the USN must do this. A concentrated IJN can wait and pounce on a split USN. The Atlantic fleet must steam up the coast or the USN Pacific flee must flee down the coast to meet this force and thus leave the west coast undefended.

The early war U.S. tanks would have been little more than burning wrecks without control of the air. The Japanese would have done to the U.S. what we did to the German tanks in Normandy. Don’t forget that the Japanese lost to no less than Gen. Zhukov in that battle with the Soviets. We did not have a Guderian. We built a mechanized army long before we knew how to use it.

The Zero was the best fighter in the world not just the best carrier plane. The P-40 and P-39 were no match, read some history. Only experienced pilots like those in China had learned how to survive against Zeros. The tactic they used was that if you had altitude and if you surprised the Zero, then you could dive on them from behind and get in one attack. Then you must immediately use the speed boost from the dive to break away before you got shot down. Of course, you can’t exactly do this if you are escorting bombers to a target, or if you don’t have surprise, or more altitude, or if you have to stay around and say, actually defend ground troops or something like that. The information that they had sent to the U.S. was largely ignored by racist officers who refused to believe the Japanese could even build such a superior aircraft. Actually, most American officers from MacArthur on down totally underestimated the Japanese. Imagine that!

The U.S. invaded a strongly defended fortress where the fortifications had been constructed for years on Okinawa. The Japanese would not face anything like what was on Okinawa. The size of the Okinawa task force proves nothing. The Japanese took Luzon when they were out-numbered 3:2. The U.S. force on the west coast would be spread out over 1200 miles and the Japanese would be concentrated at the point of attack. The Japanese wouldn’t be waiting on the beaches like we did at Anzio. They would be driving all over as they did throughout the Pacific.

People keep arguing with a U.S. military that would not exist for months or even years. How would the military in March 1942 stop an invasion? The Japanese had a window of opportunity where they could savage the U.S. to the detriment of the war effort against Hitler. Even you suggest that the U.S. would just scorch one quarter of our aircraft industry along with the west coast and sacrifice millions of citizens as though this is a solution. Yes, we win against the Japanese, if we want a Nazi Europe. Nothing you have said would convince FDR to destroy half the country rather than sign a truce.