Pearl Harbor - A conspiracy that will live in infamy?

The Japanese Imperial navy, under the direction of the fascist government in Tokyo and the command of Admiral Yamamoto, launched a surprise attack on the US base early on the morning of 7 December, 1941.
Yamamoto's fleet of six aircraft carriers had advanced into the waters surrounding the Hawaiian islands two weeks before, establishing a base to launch a full on assault with more than 400 planes targetting Pearl Harbor.
A wave of bombers from the Japanese ships into targets across the main Hawaiian island of Oa'hu was launched just before 7am.
Aerial bombardment paralysed the US aircraft at Ford Island and Wheeler Field, leaving Pearl Harbor exposed to a bombing raid by the Japanese air force.
Almost 200 planes took to the skies over Pearl Harbor in the first wave, and a similar number followed in a second string of attacks, and rained down fire on the key naval base.
Around 2,400 US sailors lost their lives in the onslaught, which lasted little more than two hours.
The pride of the US pacific fleet, the monstrous battleship Arizona, was sunk by an armour-piercing missile, entombing 1,177 military men under the waters of Pearl Harbor.
In all the fleet lost five battleships, including the heavily armoured Arizona and Utah.
The fleet's air craft carriers were not in docks at the time of the Japanese attack, but two destroyers and 188 air craft were obliterated.
As a result of its scale, and its sheer disregard for the conventions of warfare, the siege of Pearl Harbor led to an outraged reaction by the American public.
President Franklin D Roosevelt declared it "a date that will live in infamy", and quickly sent his nation to war with the Japanese.
The attack also provided political cover in the US for the President's previously unpopular support for American intervention against Nazi aggression in Europe.
Pearl Harbor not only marked the turning point in the war in the Far East, but ensured the US would send troops to Europe to stave off the German march across the continent.

The central conspiracy theory is that commanders on the ground were denied crucial intelligence on the Japanese attack in order to provoke a war with Japan and Germany.
Theorists have used declassified documents and Freedom of Information legislation to show that some branches of the US government did have a degree of prior knowledge about the attack.
One of the most important documents to come to light is the so-called "McCollum memo".
Sent on October 7, 1940, by naval intelligence officer Arthur McCollum to Navy chiefs Walter Anderson and Dudley Knox, two of President Roosevelt's most trusted military advisors, it details an eight step plan for provoking Japan into "an overt act of war".
To many theorists, the fact that the US army's Signals Intelligence Service and Office of Naval Intelligence had already broken many Japanese codes is clear evidence that the government must have known about an impending attack.
By late 1941 cryptographers had even deciphered "Purple" the highest clearance Japanese code.
The conspiracy is said to have revolved around the intelligence services accessing the plans for Pearl Harbor, but failing to pass that knowledge on to Admiral Kimmel and General Short of the pacific fleet.
If the theory is to be believed, it was this act which cost 2,400 sailors their lives, but helped Roosevelt to turn the war in Europe in the allies' favour.

- The McCollum memo. Though not quite the "smoking gun" that many conspiracy theorists believe it to be, the memo does show that the US government was attempting to provoke a Pearl Harbor-esque attack.

- The Purple code. With access to the most sensitive information the US should have been able to at least pick up that an attack on Pearl Harbor was imminent. The fact that none of this was passed on is suspicious.

- Phone taps. The US were listening in on all calls between the Japanese embassy in Hawaii and Tokyo. Surely this would have given them advance knowledge of the attack?

- War warnings were sent out in early November 1941 to let all pacific fleet posts know that combat with Japan was imminent. Given the grave nature of these warnings, the failure of radar operators and commanders at Pearl Harbor to realise that an attack had been launched is inexplicable.

- Enterprise, Lexington and Saratoga, the three aircraft carriers based at Pearl Harbor, were all out of port when the Japanese struck. If the US had lost these ships, it could have spelt disaster for their efforts in the Pacific. The fact that Enterprise returned late from its posting (it had been due back the day before the attack) is seen as evidence that the government moved its most valuable ships out of docks to save them from a raid it knew all about.

- Radar operators did track a large number of aircraft approaching Pearl Harbor and reported it to the base. The warnings were ignored. Was this because the base was aware of the attack and had been told to ignore all warnings?

- What appears to be collusion and even deliberate efforts to allow the attack to take place, could just have been incompetence. The intelligence services worked in a sporadic way and disparate agencies rarely managed to combine to any great effect. Lots of pieces of the intelligence jigsaw were in different departments, resulting in a failure of intelligence rather than a dastardly conspiracy.

- The Japanese were highly adept at changing their codes and the JN25 code, which was used by the navy, was not cracked until after the attack on Pearl Harbor. It is possible that the Imperial Navy had realised that "Purple" was compromised and switched all discussions over the attack onto JN25.

- The tapped phones at the Japanese embassy would have been little use if the embassy staff were aware of them. This was clearly the case, as the bugs were disconnected by staff in the week before the Pearl Harbor attack.

- Though war warnings were in place, the main threat was perceived to be against US assets inside the theatre of war in the Far East. The attack on Pearl Harbor was a surprise mostly because it took place on US soil, not because it was launched by the Japanese at a time of heightened security risks.

- The three aircraft carriers were all out of Pearl Harbor on standard pre-planned missions. Saratoga was having a refit, while Lexington was delivering aircraft to Midway Island. The supposedly "fishy" delay in the return of Enterprise was due to weather conditions, not a complex government conspiracy.

- Radar intelligence on the approach of the craft was dismissed by Lt Kermit Tyler, an inexperienced officer, as he had been told to expect a large deployment of planes coming in from the mainland. He simply believed they were friendly aircraft, a human error rather than a deliberate act.

The sheer enormity of what happened at Pearl Harbor has led many to believe that someone, somewhere in the US army, must have had advance knowledge that an attack was being planned. If all intelligence and cryptographical services within all allied countries had been working as one homogenous unit then there is a chance that the US government might have known about Pearl Harbor in advance. However, this was simply not the case. The fact that the attack was carried out was due to failures in the intelligence system. It was not a callous act by a President hungry for war in Europe. There is no compelling evidence to prove that Roosevelt deliberately sacrificed his own men.