Battle of Midway June 3 - 6, 1942

Though the dates of the battle are as set out above, the groundwork was laid out long before, as set out in Mark Munson's THE BATTLE OF MIDWAY: THE COMPLETE INTELLIGENCE STORY:

At the root of the American victory at Midway was U.S. Navy intelligence successfully breaking Japanese codes and discovering the Japanese Navy’s plans to attack Midway Atoll.

Station Hypo was the team of U.S. signals intelligence (SIGINT) analysts led by then-Commander Joseph “Joe” Rochefort. Immediately after Pearl Harbor, Station Hypo began attempting to decode messages transmitted using the JN-25 code. By late April, Rochefort’s team assessed that the Japanese were planning major operations against the central Pacific and Aleutians. In a famous trick, Pacific Fleet Commander Admiral Chester Nimitz approved a ruse proposed by Rochefort that saw the American garrison at Midway send a fake message “in the clear” (on open channels) regarding broken water evaporator units on the island. Almost immediately afterward, American listening posts intercepted Japanese transmissions mentioning the water shortage and the need to bring along extra water to support the operation. The identity of the Japanese objective was conclusively determined as Midway.

Then it became a matter of positioning the remaining U.S. Pacific forces in a position to engage the enemy.





Much more on the battle at the Navy History and Heritage Command here.

Source

More here, apparently written when the breaking of the Japanese codes was still highly classified, th

fter leaving Pearl Harbor, these two task forces refueled at sea and effected their rendezvous northeast of Midway on June 2d. The combined force then proceeded under the command of Admiral Fletcher to an area of operation north of Midway.

On full consideration, it had been decided not to employ the battleships on the West Coast in defense of Midway. To strike at long range at the enemy carrier force was deemed imperative, and it was therefore thought unwise to divert from the forces supporting our carriers the ships which would be necessary to screen battleships.

Admiral Ernest J. King, Commander in Chief, United States Fleet, believed that the Japanese plans were designed to trap a portion of our fleet. For that reason he directed that only strong attrition tactics be employed, and that our carriers and cruisers not be unduly risked. To understand the Midway Battle, one should remember that our naval forces operated under a conservative policy necessitated by the superiority of the enemy's force, and under the restraint imposed by the defense of a fixed point.