Believe it or not, a LOT of information from WWII hasn't been disclosed. We still have a lot of stuff (especially around espionage & the Manhattan Project) that is under lock and

key. That said, the US was the junior partner in intelligence during WWII and we depended a great deal on the UK for how intelligence was obtained and refined.

I know this sounds totally crazy, but espionage (like sharp shooters) was considered a dishonorable thing and the US looked down its nose at the former. Brits, having invented the modern spy agency (MI5 - domestic & MI6 - external)† were the senior partners in intelligence until the 50's at least.

Spy networks take eons to develop. One of the greatest ones in the USSR was cultivated by the Brits when the Czars were still in power and that network remained viable well into the Cold War. The Brits were just way better at it, having two generations of refined techniques and considerable investment. The US had the money and was the whipper-snapper during WWII.

Because of this, the US didn't have many assets on the ground. Because of the technology available to the US and UK (and the money available from the US), they used their considerable resources at cracking the Japanese diplomatic communications codes. And it worked. By the end of the war, the US was decoding Japanese cables so thoroughly that it had to pretend to not know everything for fear of tipping the Japanese High Command off.

Defend the Realm - Christopher Andrew; a magnificent read if a bit quixotic if it's not your passion.

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