An intelligence breakthrough allowed the U.S. Navy to prepare for The Battle of Midway.

Background:
During WWII, the U.S. Navy’s codebreakers had been working diligently to decipher the Imperial Japanese Navy’s JN-25 code, a primary communication code used by the Japanese fleet. By 1942, they had made significant progress and were able to read portions of the Japanese transmissions, though not everything.

The “AF” Ruse:
In the lead-up to the Battle of Midway, the U.S. had indications, through their codebreaking efforts, that the Japanese were planning a major operation against a location coded as “AF.” The U.S. Pacific commanders suspected that “AF” might be Midway Atoll, but they needed to be sure.

To confirm this suspicion, the U.S. base at Midway was instructed to send a message in the clear (i.e., unencrypted) stating that they were having freshwater problems. The hope was that the Japanese would intercept this message and then transmit it in their own code.

The ruse worked. The Japanese sent a coded message stating that “AF” was short of water. U.S. codebreakers intercepted and deciphered this transmission, confirming that “AF” was indeed Midway.

Significance:
This intelligence breakthrough allowed the U.S. Navy to prepare for and effectively counter the Japanese assault on Midway. Having this knowledge was instrumental in the U.S. victory at the Battle of Midway, which took place from June 4 to June 7, 1942. The battle was a decisive defeat for the Japanese and is often considered the turning point in the Pacific War.

The use of the “AF” ruse is a prime example of the importance of intelligence and deceptive strategies in warfare. By leveraging their codebreaking skills and using deceptive tactics, the U.S. gained a significant advantage in one of the most crucial naval battles of the Second World War.

Armed with this information, the Americans moved their aircraft carriers to a position northeast of Midway, where they would lie in wait. They were now in a position to stage an ambush on any arriving Japanese ships.

Interesting fact: If OP-20-G had not discovered in advance the site of the planned Japanese attack, the American carriers would have been 3000 miles away when it happened.