I’ve heard the Churchill rumors too, either as a co-conspirator with Roosevelt, or as simply waiting in anticipation for the U.S. to be thrown into his arms as an ally by the attack.
The direct inspiration for Churchill-as-suspect is likely two-fold:
His avowed willingness to do damn near anything to bring the U.S. into the war. I believe there were documented instances of British intelligence spreading outright disinformation to try to nudge the U.S. along, though I’d be hard pressed to name them, and the Axis threat was certainly real enough that Britain didn’t need to do much more than pass along the truth, with perhaps a little creative spin.
The bombing of Coventry in 1940, when Enigma decryptions revealed that the Germans would be striking at this previously untouched and largely undefended target, but Churchill directed that no warning be given or expedient defences attempted in order to avoid compromising the Enigma secret. I believe that Churchill was later quoted as having been deeply troubled at having to have made that decision, but it certainly seems like the right one, given not only the scope of the secret being protected and the rather limited difference to Coventry that any actions would have made. This incident has probably fed the opinions of neo-isolationists and Churchill-haters to the effect that: “You see what kind of guy he was? He probably knew about Pearl Harbor too!”
In any event, I find the Churchill rumor even less compelling than the Roosevelt one. As Corrodo’s response to this query points out, British intelligence sources in the Pacific were no better than American ones at the time. The one edge the British might have had regarding Japanese issues was Japan’s ambassador to Germany, who was something of a “Teutonophile” and all too willing to share information with his hosts. Even so, the ambassador had no better information regarding his governments plans, much less the navy’s, than Japanese diplomats in the U.S. In fact, as the war commenced, the Japanese embassy in Berlin proved to be a better source of information on the Germans, thanks again to U.S. knowledge of the Japanese “Purple” diplomatic code. The Germans, of course, were as shocked by Pearl Harbor as anyone else, such that British intelligence had no opportunity to get in on the secret by that route.
Finally, if Churchill had somehow known about Pearl Harbor, it seems likely that he would also have had some useful information about Japanese plans in Southeast Asia, and would have been able to warn British forces in Singapore and Malaya about the Japanese attacks which sank the Battleship Prince of Wales and Battlecruiser Repulse, and humiliatingly crushed the British garrisons in the weeks following. None of which accrued any discernable political benefit to Churchill.
I thought Corrado’s report pretty well covered the necessary debunking bases. The fact is that by the time of the Pearl Harbor attack, everybody expected an attack, but nobody expected one by carriers on Pearl Harbor. Sabotage at Pearl was an accepted possibility, as was submarine activity around Hawaii (hence the agressive pursuit of a submarine contact which resulted in the depth charging and sinking of a Japanese mini-sub hours before the Pearl Harbor attack began.
The adequacy of Admiral Kimmel and company’s preparations at Pearl is another matter for debate. A still more glaring situation, however, was that in the Phillipines. A Japanese attack there was entirely expected, and yet General MacArthur’s preparations were quite inadequate, whether due to pseudo-racist underestimation of the Japanese, or outright incompetance. I’m not sure where the evidence stacks up regarding any advance warnings to MacArthur, but if he wasn’t warned at all or strenuously enough, it still seems more likely that the intention was to protect the intelligence source, rather than to ensure that we “got hit hard enough to bring us into the war”.
On the other hand, might there have been some in the armed forces or the government who still harbored a grudge over the supression of the Bonus Marchers in '32?
On a semi-related note, my one real criticism of Corrado’s generally well stated report is with his passing contention that “Had the air raid been followed up with an invasion, Pearl Harbor could not have held out for long”. In fact, the Army garrison on Oahu was fairly substantial. More to the point, Hawaii was thousands of miles from the nearest Japanese base (Kwajalein), and thousands of miles more from the nearest major naval and logistical support base (Truk). An attempted landing of the necessary scale over that distance would probably have been beyond the capabilities of the Japanese, who were at the limits of their resources moving substantial invasion forces over the short hops from Formosa to the Phillipines and from Indochina to Malaya. If they had undertaken an invasion of Pearl Harbor, the resources required probably would have precluded their invasions of the Phillipines and the Indonesian islands (the oil of which was the whole point of going to war). Moreover, without first securing Wake Island and/or Midway, the supply lines of any force landing in Hawaii would have been threatened and a campaign of any length would likely have been untenable.
And there are a few fishy things about that Foster “suicide” too…