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CHIPS Articles: Station Hypo and its Impact on the Battle of Midway

Station Hypo and its Impact on the Battle of Midway
Navy & Marine Corps Commemorate 78th Anniversary of the Battle of Midway
By Commander, Navy Region Hawaii - June 5, 2020
In November of 1942, British Prime Minister Winston Churchill, following the German army’s defeat at El Alamein, reported to the House of Commons that “Now this is not the end. It is not even the beginning of the end. But it is, perhaps, the end of the beginning.”

The year 1942 would prove to be a watershed year for the Allied forces fighting desperately to turn the tide against their Axis enemies.

For the United States, early May of 1942 looked anything but hopeful. In the Pacific theater, the Japanese Empire now extended through the conquered regions of southeast Asia, New Guinea and vast stretches of the central Pacific. Nowhere was the seeming invincibility of the naval and military forces of Imperial Japan more evident than in the Philippines.

On May 6, at what many would view as the nadir of America’s initial defeat in the Pacific War, Gen. Wainwright was forced to surrender the remaining American forces held up on Corregidor, and Japanese dominance of the western Pacific seemed secured. But almost imperceptibly, the tide would begin to turn the very next day.

The Japanese attack on Pearl Harbor had left the U.S. Pacific Fleet crippled, but not defeated, and the United States had no intention of simply “waiting it out” until overwhelming forces could be mustered for a counter-attack.

Three thousand miles south of Corregidor lay the Coral Sea. On May 7, aircraft from the USS Lexington and USS Yorktown destroyed the Japanese carrier Shoho, thwarting the planned invasion of Port Moresby. Had the invasion been successful, Japanese aircraft from that location would have threatened the eastern coast of Australia and more importantly, the Japanese navy would have been primed for further conquest to the south. America’s limited naval forces had been used with maximum results. But the best was yet to come.

What America lacked in military assets, she made up for in crack communications intelligence and level-headed leadership. As early as May 15, Adm. Nimitz received intelligence from Station Hypo at Pearl Harbor that the Japanese intended to occupy Midway atoll, located 1,300 miles northwest of Oahu.

Once again, the commander of the Pacific Fleet made a bold and aggressive move. He knew where and when the Japanese would arrive. With supreme confidence in the skill of his Sailors and a little luck, he could ambush the strike force and turn the tables on the enemy.

On June 4, 1942, the hammer fell on the Japanese navy. Dive bombers from the carriers Yorktown and Enterprise destroyed Japan’s frontline carriers Hiryu, Soryu, Akagi and Kaga. All four had participated in the attack on Pearl Harbor just six months before, and all four now lay at the bottom of the Pacific. The Battle of Midway had been a decisive American victory.

As a result of the battle, the United States had crippled Japan’s ability to launch further large-scale mobile strikes against Allied forces. Midway is considered by many to be the decisive battle of the war in the Pacific. Before this battle the Japanese were on the offensive, capturing territory throughout Asia and the Pacific.

Though it would be another year before the United States’ industrial capacity began to fill the world’s battlefields with the wherewithal to crush the Axis’ ability to resist, America’s aggressive actions in May and June of 1942 halted any significant Japanese advances and bought precious time for the marshalling of the forces that would eventually roll back the enemy.

America’s military leadership understood very well that the Japanese Empire was nowhere near defeat. Many years of hard struggle lay ahead if the tough and determined Japanese soldiers were going to be pried away from their strongholds in New Guinea, the Philippines, the Dutch East Indies and the numerous islands and atolls in the central Pacific.

However, the string of humiliating and costly defeats that marked the beginning of World War II had surely come to an end. America’s victory at Midway was the first irreversible Axis defeat of the war and the beginning of the end for the empire of Japan.

Station Hypo

Just months before the infamous attack on Pearl Harbor, in the summer of 1941 a small collection of intelligence analysts, linguists and code-breakers would set up the newly renamed Combat Intelligence Unit in the nondescript basement of building 1, the administrative headquarters of the 14th Naval District.

The unit was also known by the code name Station Hypo. Hypo was charged with the collection and analysis of Japanese radio signals by which the United States hoped to keep a wary eye on the expansionist designs of the Japanese Empire.

The basement, affectionately known as the “dungeon,” was described as a large windowless space crammed with tables full of boxes containing cards and printouts from tabulating machines that would continually spit out messages intercepted from the various receiving stations around the Pacific. There was one entrance in and out guarded at all times by an armed Marine.

A brilliant officer named Cmdr. Joseph Rochefort, who worked tirelessly with his small staff, to keep abreast of Japanese intentions, led hypo. However, in 1941 the American code-breakers were still unable to read the Japanese operational code known as JN-25 and instead were forced to rely on diplomatic traffic, the inconclusive observation of ship movements and routine radio correspondence. As a result, the United States was caught by surprise when Japan launched their raid on the morning of Dec. 7, 1941. But Hypo’s finest hour was yet to come.

By March of 1942, the JN-25 code had been broken and Rochefort and his staff were determined to keep close tabs on Japan’s military forces and stay one step ahead of the enemy’s intentions. From the “dungeon” it was determined that the Japanese would launch an invasion of an undisclosed location known only as “AF.”

Rochefort reasoned that “AF” was Midway Island and that the Japanese would attempt an invasion around June 4. Many in Washington remained convinced that Japan’s next move would be toward the Aleutians, leaving Adm. Chester W. Nimitz with the difficult decision of determining how to best use his limited forces.

Once again, the answer came from the basement of building 1 when a brilliant scheme was devised to expose the enemy. A message was sent across the undersea cable instructing U.S. forces on Midway to send a false radio message in the clear stating that Midway’s fresh water system had malfunctioned.

The Japanese took the bait and soon Hypo intercepted a Japanese message stating that “AF” was having trouble with its fresh water system. Soon Nimitz gave the order to send his available carriers north of Midway to intercept the Japanese strike force and a decisive battle was won, as much by the intelligent exploitation of perceived Japanese intentions as it was by the pilots and crew who sunk four of Japan’s fleet carriers.

In April 1943 the Combat Intelligence Unit would move out of its cramped facilities at building 1 and move into a new home at Makalapa near the Pacific Fleet headquarters.

The “dungeon” would lie vacant, serve as storage spaces or administrative offices for the next several decades until its legacy was rediscovered in the last few years. There are now two entrances into the space and a plaque hangs outside each stairway to mark the important events that happened in the darkest days of America’s struggle against Imperial Japan.

Scene on board USS Yorktown (CV-5), shortly after she was hit by three Japanese bombs on June 4, 1942. Dense smoke is from fires in her uptakes, caused by a bomb that punctured them and knocked out her boilers. Taken by Photographer 2rd Class William G. Roy from the starboard side of the flight deck, just in front of the forward 5"/38 gun gallery. Man with hammer at right is probably covering a bomb entry hole in the forward elevator. Note arresting gear cables and forward palisade elements on the flight deck; CXAM radar antenna, large national ensign and YE homing beacon antenna atop the foremast; 5"/38, .50 caliber and 1.1" guns manned and ready at left. Courtesy Naval History and Heritage Command.
Battle of Midway, June 1942 A Douglas SBD-3 Dauntless scout bomber (Bureau # 4542), of USS Enterprise's Bombing Squadron Six (VB-6), on USS Yorktown (CV-5) after landing at about 1140 hrs on 4 June 1942. This plane, damaged during the attack on the Japanese aircraft carrier Kaga that morning, landed on Yorktown as it was low on fuel. It was later lost with the carrier. Its crew, Ensign George H. Goldsmith, pilot, and Radioman 1st Class James W. Patterson, Jr., are still in the cockpit. Note damage to the horizontal tail. Courtesy of Kent Walters and Robert J. Cressman.
Alongside the Sand Island pier, Midway, disembarking Marine reinforcements, 25 June 1942. Aircraft in the foreground, with damaged tail, is a TBF-1 Avenger (Bureau # 00380), the only survivor of six Torpedo Squadron Eight (VT-8) TBFs that attacked the Japanese fleet on 4 June 1942. Ship in the right distance is probably USS Ballard (AVD-10). Official U.S. Navy Photograph, now in the collections of the U.S. National Archives.
U.S. Navy Captain Joseph John Rochefort. Photo courtesy of NSA.
An artist rendering of Midway Island as related to its location to the continental United States, as part of the Hawaiian Island chain and a detailed image of the island itself.
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