The Hypo “Dungeon”
U.S. cryptographers at Hawaii’s station Hypo (the British military designation for “H” for the Heeia radio post) had managed to decipher much of the Japanese Navy’s most important code, dubbed JN-25. Working in a windowless basement they called “the dungeon,” the codebreakers under the direction of the brilliant Commander Joseph Rochefort, noticed increased Japanese radio traffic referencing a point called “AF.” It was becoming clear that “AF” was the focal point of a major upcoming operation featuring a carrier group and at least one surface fleet, and it would be executed either on June 4 or 5.
But what exactly was “AF”? In one of many instances of Dame Fortune smiling on the Americans, it so happened that in March a Japanese aircraft reported its position as being near “AF”. Plotting the plane’s location, the only significant land mass in the area was Midway. Hypo had no doubts what this meant. But Washington was not so sure, fearing moves toward Australia or even Hawaii itself. To confirm that the all-important “AF” was, in fact, Midway, Rochefort’s men devised a clever ruse. They submarine-cabled instructions that Midway should radio, un-coded and in the clear, a bogus message that the base was suffering a fresh water shortage due to a malfunctioning desalinization system. The Japanese fell for it, and two days later station Hypo was deciphering enemy radio traffic deeming contingencies be made for extra water purification systems to accompany the landings as “AF” was suffering a fresh water shortage. “AF” had to be Midway. Now Nimitz knew where, as well as when and with what, Yamamoto would make his next move. But how to prepare for it?
After considering the options Nimitz opted to take a calculated risk by sending his three remaining carriers to “Point Luck” 320 miles northeast of Midway to lie in wait for Nagumo’s unsuspecting carriers as they steamed into the area from the northwest. Given the superiority in firepower and tonnage of Yamamoto’s trailing main body, the operation would be hit-and-run against the all-important carriers, while avoiding any surface engagements. What slower battleships remained were sent to the West Coast for the duration. 0
Task Force 16, with Enterprise and Hornet, six cruisers and eight destroyers set sail on May 28, under the command of Rear Adm. Ray Spruance; Halsey, hospitalized with a severe skin condition, would miss the second major naval engagement in as many months. The patched-up Yorktown and Task Force 17 with two cruisers and five destroyers followed two days later flying the flag of the two forces’ tactical commander, Adm. Fletcher. Nimitz remained at Pearl Harbor and stayed in contact by radio. If Fletcher and Spruance could catch Nagumo’s carriers at the right time, just as they were either launching or recovering aircraft, with the element of surprise—and a little luck—they might just pull off a devastating attack. The Japanese, believing the U.S. carriers wouldn’t appear on the scene until well after the first attack on Midway, had no idea the tables had turned, and they were the ones sailing into a trap.
Brad Schaeffer is an historian, author, musician, and trader. His eclectic body of writings have appeared in The Wall Street Journal, New York Daily News, and a variety of well-read blogs and news outlets. Of Another Time and Place is his first novel, which takes place in World War II Germany and the deadly skies over the Western Front. You can pre-order his book here: