“... There was no clear, unambiguous signal saying attack Pearl Harbor. ... indicators that point to an attack, but hindsight is 20/20. If FDR had known about the attack, he could have done a better job of absorbing it, and would have been in a position to inflict great damage on the Japanese early in the War.
... What if the Japanese had invaded the unprotected beaches of Hawaii a few days after Pearl Harbor, supported by aircraft carriers and naval gunfire, possibly taking the Pearl Harbor out of U.S. hands, and possibly even seizing significant oil reserves?”
Cryptanalysis is more difficult than many casual observers can appreciate. The Allied (in reality, Polish/British/US) successes in this field came later in WWII: in 1941, none of the infrastructure nor procedures existed. Anyone who thinks - even for so long as a millisecond - that it was even possible for the US government to discover what Imperial Japan was up to, is committing the most grievous errors imaginable.
Gordon Prange (and his inimitable co-authors, whose names refuse to return to my memory at the moment) has shown conclusively that no actions the US could have taken would have influenced Imperial Japan one way or another: the decision to go to war was taken by the Japanese leadership.
Recent analyses and informed conjecture have conceded that no amount of tactical warning could have saved US forces from the mauling they endured on 7 December 1941, and the days immediately following. There simply were no command and control systems to receive alerts, assess attack strength/objectives, assign defense assets, or direct them in battle.
All speculation about “what might have happened” is of course uncertain, but it’s quite possible that had the USN Pacific Fleet sortied from Pearl Harbor in time to meet the oncoming Imperial Japanese Naval attack fleet in a full-scale open-ocean battle, the results would have been far worse for the Americans. And every vessel lost in that clash could never have been salvaged, sunk as they would have been in deep water.
What truly cooked the American goose that day was lack of air-mindedness on the part of local commanders: the US Navy was preparing to meet a naval attack, and the US Army was preparing to meet a ground attack (an invasion force, as Lonesome in MA suggested). Never the twain did meet.
And - most ruinously - blinkered thinking could not be blamed on personal flaws of local commanders. Both Walter C. Short and Husband E. Kimmel were products of their separate service traditions and corporate culture. Their approach to waging war, while admirably traditional, was outdated decades before. The late Billy Mitchell predicted so in hideous detail in the 1920s, and moreover had the bad manners to prove it.
And no one can guarantee that blunders on such a scale can never descend on us in the future, as we persist in clinging to brainlessness ... the family of Admiral Kimmel persevered in petitioning the Navy Dept to get his name cleared, and USN leadership agreed at last. Family members of William Mitchell have made several attempts to get his court-martial conviction reversed, but in inexplicable contrast, DoD has always turned them away.
You know, a really good short story (can’t recall what compilation it’s a part of) is called “Billy Mitchell’s Overt Act”, which has him remaining in the Army following his court martial and ending up as the CO of USAAF in the Hawaiian Islands leading up to Pearl Harbor ...