Stemming the Tide of Japanese Expansion

   The first major action in which U.S. Navy’s radio intelligence provided a significant part was the recognition of Japan’s Operation MO to occupy Port Moresby and the resultant Battle of the Coral Sea.  As early as 3 April 1942, Hypo reported an impending offensive from Rabaul.  Negat informed Admiral King that air search patterns clearly indicated an interest in the Coral Sea on 7 April.  Next, Hypo reported a light carrier leaving Truk for the Coral Sea on 14 April.  The same day the British at Anderson were more specific in warning that the First Air Fleet appears to be connected with an operation against Port Moresby without any date or details.  By 16 April, the ONI desk in Washington surmised that carriers may be directed against the Australian sphere.  Upon Nimitz’s assumption of command of the Coral Sea area on April 17th, he held a review with his Intelligence Chief, Captain Edwin T. Layton.  Rejecting Melbourne’s predictions that the Japanese might move as soon as 21 April, Nimitz felt the IJN could not assemble its forces until the first of May.  Nimitz ordered Rear Admiral Frank “Black Jack” Fletcher to have the Lexington and Yorktown ready for a fleet action in the Coral Sea in early May.

   Towards the end of April, Cast and Hypo were able to decrypt messages that detailed the organization of MO’s carrier strike, covering, and occupation forces.  On 3 May, Hypo reported the gist of Fourth Fleet’s general orders to the carrier strike force commander, Admiral Takagi. On 5 and 6 May, there were messages from Admiral Kajioka’s MO Occupation Force giving his position and plans for sailing south on May 7.  Also on 5 May, Fletcher learned that Takagi’s strike force would be in a given position at 10:00 A.M. that day.  This gave Fletcher time to avoid Takagi after the previous morning’s air strikes on the Japanese invaders of Tulagi.  After an U.S. carrier search plane had miscoded a sighting report of two cruisers and two destroyers to read two carriers and two heavy cruisers on 7 May, Lexington launched her attack planes at 9:26 A.M. and Yorktown followed later.  As a result, the small carrier Shoho was sunk.  The Japanese were also the victim of a sighting report from a scout plane reporting a carrier and three destroyers for the oiler Neosho and the destroyer Sims.  Planes from Admiral Hara’s Carrier Division 5 attacked these ships sinking the Sims and leaving the Neosho a floating wreck.  On two occasions, Fletcher ignored information provided by Lieutenant (j.g.) Forrest Biard of his own RIU locating Hara’s carriers and following erroneous information provided by Ensign Fullenwider, head of the Lexington’s RIU, even though the latter’s error in one case was easily explained.  As a result, an attack was made on the small carrier Shoho leaving the Zuikaku and Shokaku free to later attack the Lexington and Yorktown.  Subsequently, on 8 May, the Lexington was sunk and the Yorktown was damaged.  The Shokaku and Zuikaku were hit badly enough to sent them to Japan for repairs keeping them out of the Midway MI operation and possibly changing the outcome of that battle.  The presence of U.S. carriers and the sinking of the Shoho caused the Japanese occupation force to return to Rabaul and saved Port Moresby as an important Allied base.  Radio intelligence on naval targets, which later went by the codeword Ultra, had proved itself an important factor in turning the strategic outcome in our favor.  Nevertheless, a commander who did not fully appreciate the use of tactical radio intelligence could still make serious errors.  It is understood a new biography of Admiral Fletcher soon to be in print attempts to rehabilitate him to some degree.

   The best known accomplishment of naval intelligence in the war with Japan was the discovery of the IJN plans to attack Midway Island.  Even the movie “Midway” has a fair level of accuracy.  However, it must be covered again in this historical review.  The achievements of then Commander Joseph Rochefort and his crew at Station Hypo cannot be overemphasized.  Prior accomplishments of Cast and Negat also contributed to this success.  Even before the Coral Sea engagement, Rochefort predicted a major Japanese effort against the Central Pacific.  Hypo was intercepting about 60 percent of JN-25 messages at that time and only 40 percent of that was being read to any degree.  Recoveries of the geographical designators for the Aleutians, Pearl Harbor and Midway helped in this assessment.  The delay in shifting the new version of JN-25 (JN-25C) to late May allowed the U.S. radio intelligence community to read many of the changes to Operation MI details.  A 16 May message by Admiral Nagumo revealed an intention to stage air attacks from a point fifty miles northwest of “MI” two days before the invasion.  Midway Island was again compromised as AF, Operation MI’s target, in a 22 May message.

   The Japanese plan to refuel long range seaplanes from French Frigate Shoals for reconnaissance per past practice was further frustrated when a message was decrypted indicating reemployment of this K Operation.  This information was passed to Commander Layton, who worked closely with Rochefort and Hypo personnel.  Layton passed this to Nimitz who reinforced the small detachment at French Frigate Shoals with the seaplane tenders Thorton and Ballard.  When a Japanese submarine saw these ships at anchor, Operation K’s seaplane reconnaissance of Pearl Harbor and its environs was cancelled and the U.S. forces deployed to the Midway area undetected.

   Nevertheless, there were important differences between Rochefort and Washington, including fears the attack would be southward, Hawaii, Aleutians or the West Coast.  Then, the Melbourne unit of formerly Cast personnel began to back Rochefort’s predictions.  Finally, by 17 May, Admiral Ernest J. King Fleet Commander in Chief (COMINCH) advised Nimitz he now agreed with Nimitz that Midway was the target of the Japanese fleet and occupation force despite Washington’s remaining fears of a bona fide attack on Alaska.  The much publicized ruse of having Midway send a message in the clear that it had problems with its fresh water evaporators was only to satisfy Washington’s doubts.  Finally, Yamamoto’s long final operations order on 20 May was worked on through the night by Hypo to provide Rochefort with a clear picture of the MI plan.  On 25 May, the long delayed change to the new JN-25C was effected greatly limiting the information available.  However, on 27 May, Rochefort was able to brief Nimitz on the complete plan including disposition of Yamamoto’s forces including the 3 June diversionary attack on the Aleutians before hitting Midway the next day and followed by the occupation forces.  CINCPAC staff officers couldn’t believe what they were hearing and tried to say it was a ruse, but Nimitz would not be dissuaded.  Layton’s estimate of 4 June with the attack coming from the northwest bearing 325 degrees with a sighting 175 miles from Midway about 6:00 A.M. Midway time was only five miles, five degrees and five minutes off.  Elsewhere on this web site, the details of the Battle of Midway can be found.  The Japanese lost the carriers Akagi, Kaga, Soryu, and later the Hiryu.  In addition, they lost the cruiser Mikuma.   The U.S. lost the carrier Yorktown and the destroyer Hammann.

   U.S. Navy officials were stunned to read the Chicago Tribune story by Stanley Johnson that the Battle of Midway was won in part due to the breaking of the Japanese naval code.  An investigation disclosed that Commander Morton T. Seligman, the former executive officer of the Yorktown, had shared a cabin with Johnson on the transport Barnett and permitted Johnson to see classified documents.  To preclude further publicity, no criminal charges were made but Seligman was barred from further promotions.  Fortunately, the Japanese did not have access to the Chicago Tribune.  Apparently, they were only interested in the New York Times, Washington and West Coast newspapers.

   Despite his tremendous achievements, Joe Rochefort paid the price of showing up Washington and the newly installed cabal of the Redman brothers.  The senior Redman brother, Admiral Joseph R. Redman, replaced Noyes as DNC.   Captain Safford was ousted and Redman’s younger brother, Commander John R. Redman, untrained in intelligence and codebreaking, was installed as OP-20-G.  In October 1942, the Redmans’ efforts to remove Rochefort to a sea billet since June was accomplished.   Only near the end of the war was he brought back, but for a strategic intelligence unit within COMINCH.   What a waste of a priceless talent for a political payback.  Nimitz’s recommendation for the Distinguished Service Medal for Rochefort was twice denied, but given to political cronies of the Redmans in Washington.  Nimitz was right when he said there was going to be a major war and those in sea command billets would be blamed and those in Washington command positions would prosper.  He was omniscient enough to turn down the Pacific Fleet job for a Washington billet before Pearl Harbor.

   On 25 June, Nimitz commended the Pacific High Frequency Direction Finder (HFDF) Net for its “incalculable aid” to him and the forces in the combat area.