Learning Pearl Harbor: What was the Kido Butai?

Formally known as the First Air Fleet of the Imperial Japanese Navy, kido butai—meaning "mobile force"— was the strike force that attacked Pearl Harbor on December 7, 1941. The astonishing feat of sending this huge, carrier-based force undetected across the Pacific to within 230 miles of the island of Oahu is an incredible story.

An Enormous Gamble

The concept of employing a stealth mobile force to preemptively attack the US Pacific Fleet came from Admiral Isoroku Yamamoto. The attack was considered by many to be too dangerous a gamble.  Fittingly, Yamamoto was known as a gambling man, but he was also a highly respected Japanese naval strategist. He eventually persuaded the Japanese leadership to go ahead with the risky attack.

One reason that it was so risky was the significant possibility that American bombers would locate and attack the kido butai before it could reach its destination. Rather than delivering a devastating blow to the US, such a strike would make the already tense situation in the Pacific much worse for the Japanese.

The risk was even greater because of the distance from the nearest Japanese base. It would not be possible to tow a damaged aircraft carrier back to a base.

In addition to the risks, there were also numerous logistical difficulties for the First Air Fleet to travel such a distance. They chose a route that would leave them undetected, but it was both a longer distance and worse seas.  They had to refuel at sea in stormy sea conditions. All ships, commercial or otherwise had to be avoided to prevent detection of the fleet.

Despite all of the risks and difficulties, Kido Butai successfully arrived 230 Miles North of Pearl Harbor undetected and departed before the US Navy could catch her.

Led by Vice Admiral Chuichi Nagumo, Kido Butai consisted of six aircraft carriers, the largest number of aircraft carriers ever to operate together; two Battleships, two heavy cruisers, nine destroyers, eight oil tankers, and twenty three submarines. On the decks of the submarines were two-man midget submarines. Kido Butai had 414 airplanes including zeros, Kate bombers, and Val dive bombers.

Nagumo chose to abort the third wave of the attack in order to protect Kido Butai from a counter attack. This decision has been criticized by others within the Imperial Japanese Navy as well as many historians.  The third wave could have targeted other strategic locations including Pearl Harbor's oil tanks, the shipyard, and the submarine base.