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Pearl Harbor

The main theme with this event is lack of action on sufficient information. Most of the government groups here had more than enough information to be able to deduce that there was at least a major threat coming from Japan. None were able to properly acknowledge this as a real threat and prepare for it.

While there was a lot of noise at the time, Wohlstetter states

despite all the noise that accompanied the warning signals, it was unreasonable for the Navy group to have omitted its own base at Pearl Harbor from the list of possible Japanese targets. pg. 86

It's not that other targets were chosen as higher risk, its the fact that Pearl harbor wasn't even considered.

Short term evidence of an attack

These are just a hand full of examples of the mound of evidence pointing towards a Japanese attack.

Nov 16 1941: lost track of japanese aircraft carriers Dec 6 1941: Intel that japanese consulate was burning papers Dec 7 1941 @ 6:53 am: Submarine Dec 7 1941 @ 7:02 am: Spotted fleet Dec 7 1941 @ 7:55 am: Bombs drop

Somewhere in November there was also a warning from the US ambassador (?) in Japan saying they knew that Japan was preparing for an attack and that it was very possible it could be against the US. That they were willing to commit political suicide to stop themselves from being the target of any more economic embargoes (pg. 98)

Japan's incentive

Japan already had an embargo placed on it from European countries (due to Japan's alliance with Italy and Germany) and the US placing a similar embargo put Japan in a very bad position. They could either let this happen, lose all the progress they had made in Asia, and submit to the powers admitting they were weak and could be manipulated like this... or they could take a stand.

Janis makes an interesting point about perspective. He brings up the fact that everyone was calculating the risks of each move for the US, but

no one discussed anticipating enemy moves from the standpoint of how the Japanese would view the risks of not attacking the US. pg. 88

Symptoms of Groupthink

These are a list of assumptions and convictions based on stereotypes that can be viewed as symptoms of groupthink. Stereotypes about Japan influenced their decisions and drove their culture around thinking about attacks. They considered Japan too weak to retaliate or even consider attacking the US.

The fleet at Pearl Harbor was enough to deter any attack from Japan

It wasn't considered that this might be seen as a target...

Even if the Japanese were foolhardy enough to send their carriers to attack us, we could certainly detect and destroy them in plenty of time

It wasn't considered there might not be any warning at all, and certainly nothing was done to ensure these warnings would exist.

In fact, the day before the attack training was chosen over recon for the planes because there was more concern over an internal attack (sabotage or an attack on foreign territory.

No warships anchored in the shallow water of Pearl Harbor could ever be sunk by torpedo bombs launched from enemy aircraft.

It wasn't considered that Japan might have invented a new type of torpedo that could perform well in shallow water.

Japan would first direct its attack against weaker targets like the British and Dutch territories before attacking a super power like the US

But they didn't consider Japan might be trying to stay in the super power game.


  • Jokes were made about Japan's incapability to attack the US. This kind of joking reinforced the stereotypes.
  • During the weeks coming up to the attack the base was on open weekend leave. It would have been very difficult for anyone to bring up concerns about an attack and be the one that ended such a luxury.
  • The Army was blowing steam up the Navy's ass saying they felt comfortable just knowing the Navy was near by... Reinforcing the assumption that a fleet was protection not a target.
  • Conflicting personal and formal information from Washington made it seem like there was no real threat from Japan. On 24 and 27 November, a list of targets that Japan might attack were handed out, Hawaii was not one of them.
  • Vague terms were used like "an attack on pearl harbor is not highly probable" which was interpreted as "not probable". Use of vague predictions is a pitfall mentioned in Superforecasting


I think the main point Janis is trying to get across with this chapter is that all members of leadership were strongly reinforcing stereotypes and assumptions about the enemy. This lack of objectivity made it incredibly hard for anyone to speak up about concerns in regards to an attack from Japan.

Other notes

  • AGIC was an intel project that was decrypting and following Japanese radio messages. They knew Japan was getting ready for a major attack and even got threats that it would be against the US but they were ignored.
  • conspiracy theories that the US let the attack happen in order to rally support to enter WWII Hanlon's Razor