JwAs for Pearl Harbor, there are basically 2 questions that can help us determine whether it was an inside job (of the third type) or not.
- Was the Japanese code cracked prior to the attack on Pearl Harbor?
- Did the Japanese planes approaching Pearl Harbor maintain radio silence with one another?
If the answer to question 1 is "yes, the code was already cracked" and the answer to question 2 is "no, they did not maintain radio silence," then Pearl Harbor was an inside job. It means officials saw the attack coming and let it happen. As it turns out, it is 100%, without a doubt the case that the Japanese code was cracked (so we knew what they were saying to one another) and that the Japanese did not maintain radio silence. This is a summary of the case that Pearl Harbor was an inside job, and it's basically as strong of a case as the JFK assassination, 9/11 being an inside job, etc.
Except it is known that the IJN was able to skirt past Americans specifically because they maintained complete radio silence (as dictated by Yamamoto) and followed a route that was out of the way of American bases. Even so, it was due to radio deception by the Japanese leading up to the war and the dismissal of a Oahu-based radar which picked up the approaching planes that allowed the Japanese to get so close without being spotted. We know this because of information + PoWs obtained during the war as well as information being decrypted and translated during the postwar period. You can watch YouTube videos online of Japanese pilots stating exactly how they prepared for and attacked Pearl Harbor.
Also, as previously stated, claiming Americans had already cracked the Japanese’s code prior to Pearl Harbor is only partially true. There was no singular code during the war; the Japanese were aware of American/UK code breaking abilities and took great care in utilizing several different codes throughout the conflict. Americans were able to crack many of their codes such as Purple, but many remained unsolved at the time of the attack, such as JN-40.
US was already involved in Europe in many ways to the point Roosevelt had even implemented a “shoot on sight” order for US ships due to U-Boat aggression and had the lend-lease agreement going for almost a year at this point. It is ridiculous to suggest that the United States would intentionally sacrifice one of their most vital tools for winning a war (several naval bases in the pacific (Guam, Philippines, and wake island were also targeted in the attack)) just to enter said war. Especially when the tripartite pact was essentially a defensive agreement, meaning that the US orchestrating an attack on themselves would not only jeopardize their abilities to wage a naval war with no guarantees of actually entering world war 2 in the first place.