Japan’s hopes was that after destroying the Pacific Fleet at Pearl Harbor, Hawaii, that it would take at minimum 2 years for the US to rebuild the fleet back up to seriously take on the Japanese fleet.
Fortunately for us, the three air-craft carriers that were apart of the Pacific Fleet were out to sea, each on their own mission. The USS Lexington and Task Force 12 left Pearl Harbor on December 5th to deliver 18 SB2U Vindicator Dive Bombers designated VSMB-231 to Midway Island. USS Saratoga was in San Diego in order to embark her air group that had been training ashore during her refitting.. And USS Enterprise left Pearl Harbor on November 28th to deliver VMF-211 to Wake Island.
Japan’s plan was basically knock out the US fleet leaving them the dominant unchallenged power for at least 2 years. During this time Japan would conquer Dutch East Indies (Indonesia) and Malaya for their oil and rubber. Not to mention the many other islands and coastal territories that they conquered in order to gain access to other resources to build and maintain their military, such as coal and iron.
Once they’ve secured the necessary resources to continue to become self-sufficient, Japan would heavily fortify every island territory. The Japanese military leaders (who ignored the warnings of Admiral Isoroku Yamamoto that there was no way to win a war with the US), believed that by doing this they would ensure their victory against the US. The idea was that by heavily fortifying every island would cost the US thousands to tens of thousands of casualties in order to just take one island. Even if the US defeated the Japanese defenders, Japanese military leaders believed that the cost to take one island would be considered too great and eventually the US would come back to the negotiation tables with much better terms for them.
However, Japan underestimated the US’s industrial ability. Prior to the start of the war, the US only had a total of 352 US Navy vessels operating in and around US territories; the Pacific Fleet itself consisted of less than half of that, 172 ships. It took the US less than a year to not only rebuild enough ships to fill the US Pacific Fleet, but by the end of the war the US Navy was operating 6,768 ships. Where as Japan’s fleet at the start was at 401 vessels.
They also underestimated the American people’s determination. Instead of being demoralized, like the Japanese military leaders believed would happen, it energized and encouraged Americans from across the country. Within weeks, there was over 1 million volunteers. By 1944, the US military was a 12 million man powerhouse… just an fyi, the USSR military was also around 12 million man strong.
To summarize, the Japanese military never had any hope of winning a conventional war against the US. Even if they managed to pull off their turtle defense strategy and stockpiled enough critical resources to continue to operate, the US military would’ve eventually found a way to crack their defenses. Who knows, instead of just skipping one island, we might have skipped two or three