The Battle of the Coral Sea wrecked an attempted Japanese invasion of Australia and that is why it was a great victory even at such a high cost. Nimitz immediately replaced Ghormley, who was scared sh!!less, with Halsey. Nimitz ordered the Guadalcanal landing just as soon as humanly possible mostly to take the pressure off of New Guinea. The Japanese fought so hard because they knew the stakes. Victory, or defeat.
I think the thought was of ten million Aussies in the hands of the Japanese Army, the Imperial Japanese Navy having control of the Indian Ocean, no reinforcements or supplies to the Brits in North Africa, and the Russians not able to hold the Wehrmacht at all, not at all. (Stalingrad was late in the year.)
Would the Brits have accepted the deal Hitler had offered in 1940? That is, ally with Germany and keep the Empire and get the Japanese out of Australia? Remember how close the Brits came to accepting this right after Churchill took office. Remember Rudolf Hess. Remember how the Japanese treated civilian prisoners. Think of Rommel meeting the Japanese in Cairo. Think of the Wehrmacht taking the Trans-Siberian railway to Vladivostok. Think of no bombing war from England to gut the Third Reich.
Yeah, nuclear weapons. No one knew about them in 1942. That would have worked, right?
The Third Reich had a pretty fair nuclear weapon project. It was not an enriched uranium - plutonium affair, pretty strange in a way, but....
Not a physicist by a long shot, but what they were making would have played hell with New York City. The bombing survey did not even recognize the program for what it was, no gaseous diffusion plants don't you know. Bunch of academics.