US Navy breaks Japanese Code

25th May 1942: USN Crypto-analysts make crucial breakthrough that reveals Japanese plans to invade Midway and ambush US Fleet

Admiral Yamamoto in 1942, he planned to lure the US Pacific Fleet into a trap by invading Midway.

The Akagi, one of four Japanese Fleet Carriers that would be used to ambush the US Pacific Fleet, on exercise in April 1942.

In May 1942 the Japanese were supremely confident of their military capability in the Pacific. They had swept all before them and threatened Australia, Hawaii and perhaps even the west coast of America. Now they sought to bring the US Navy to battle and complete the task they had set out for at Pearl Harbor. A large force was now despatched to take the US base at Midway - and then attack the unsuspecting US Pacific Fleet when it sought to respond, in an action that would thoroughly weaken US forces for at least a year.

Midway Atoll, several months before the battle. Eastern Island (with the airfield) is in the foreground, and the larger Sand Island is in the background to the west. A strategically important staging post for both US planes and ships.

A very small group of US Navy officers would frustrate their plans. Led by Captain Joseph J. Rochefort at Station Hypo, the Combat Intelligence Unit, Pacific Ocean Areas, located at Pearl Harbor they had succeeded in penetrating the Japanese naval code and had read their whole operation order.