The Japanese had developed a code they thought 'unbreakable' by any culture. They therefore used it to communicate between planes, ships, and battle stations to help them try and win the war. They believed that they had developed the perfect, unbreakable code.
Americans found this code only when we captured a crashed plane in Alaska. Japan was planning to attack Midway, but had decided to launch a "fake attack" on Alaska as a diversion. Several Japanese Pilots bombed a base in alaska, but one ran out of fuel and crashed into a lake upside-down. The pilot was drowned, but the plane remained entirely itact. The people of Alaska brought the plane to California where it could be studied.
When the plane was shipped to California, codebreakers and other reaserchers set imediately to work trying to decipher the Japanese code. American code decipherers could decipher most of the code, but were missing one important part -- where the Japanese had planned their actual attack.
Codebreakers in California kept recieving messages ancoded with the mysterious "AF", which was a sort of codename for the location of the Japanese attack. Codebreakers puzzled over the codeword, until they decided to test if it meant Midway. Sending a message from Midway that stated "We are running low on water", their supicions were confirmed as they recieved a message saying "AF is running low on water".
By reading this message, the American air foce was ready to defend against Japan. Air carriers were stationed near the base as the Japanese launched their attack. Although american forces had a hard time finding the air base during the battle, the knoledge saved not only the airbase, but thousands of men as well.
