H-Gram 018, Attachment 2
Samuel J. Cox, Director NHHC
On 14 April 1943, multiple U.S. radio-intercept sites copied a Japanese naval message encoded in the JN-25D cipher. U.S. Navy code breakers in Washington, DC, and at Fleet Radio Unit Pacific at Pearl Harbor (also known as Station Hypo, but by then more frequently referred to as “FRUPAC”) immediately set to work trying to break the message. The already difficult process was compounded further because the Japanese had made some changes following the sinking of the Japanese submarine I-1 in shallow water off Guadalcanal by the New Zealand navy corvette Moa in late January (although at the same time, captured material brought up by U.S. Navy divers from the submarine proved very beneficial in other code-breaking efforts). At this time, FRUPAC was under the direction of Commander William B. Goggins. Goggins had no intelligence or code-breaking background, but proved to be an able officer and leader who gained the trust of the FRUPAC code breakers following the recall of the popular (and hero of the Battle of Midway) Commander Joe Rochefort in October 1942 as a result of a sordid power struggle with OP-20G in Washington, DC. Rochefort’s reward for FRUPAC/Hypo’s success in breaking the Japanese naval code before Midway was to be given command of a floating drydock. Goggins had been severely wounded as executive officer of the light cruiser USS Marblehead (CL-12) in a Japanese bombing raid off Java in February 1942; the story of how he successfully escaped from Java just ahead of the Japanese occupation is an epic story in itself.
FRUPAC was the first to decrypt some of the message, although there were still a significant number of blanks, and it took another 18 hours to get a more complete decryption and translation. Some sources credit Marine Major Alva B. “Red” Lasswell with breaking the message. As chief linguist at FRUPAC, he certainly had a key role, but it was a team effort that included cryptanalysts Ham Wright and Tommy Dyer, and traffic analysts Tom Huckins and Jack Williams, supervised by Lieutenant Commander Jasper Holmes. Junior members of the team included future Supreme Court Justice John Paul Stevens, and future Rear Admiral “Mac” Showers. This was essentially the same cast, minus Rochefort, which achieved spectacular success before the Battle of Midway. Holmes gave a heads-up to Pacific Fleet intelligence officer, Commander Edwin Layton, and, once a finished translation was in hand, Holmes and Lasswell hand-carried it to Layton, who then went in to see Admiral Chester Nimitz, commander in chief of the Pacific Fleet.
The contents of the message included the flight schedule of Admiral Isoroku Yamamoto, commander in chief of the Japanese Combined Fleet (roughly Nimitz’s equivalent) and architect of the Japanese attack on Pearl Harbor (and the disaster at Midway). Yamamoto was already on an inspection trip to Japanese bases near Rabaul and the northern Solomon Islands. The message contained precise details and timing of Yamamoto’s flight to Japanese airfields on and near Bougainville Island, scheduled for 18 April. It also contained how many Japanese aircraft would be involved: two G4M twin-engine Betty bombers carrying passengers and six A6M Zero fighter escorts.
Layton and Nimitz discussed the pros and cons of killing Yamamoto. Layton’s extensive background in Japanese language and culture made his assessment uniquely valuable to Nimitz. Layton’s view was that no other Japanese admiral had Yamamoto’s stature, experience, innovative thought, or charisma. Other Japanese admirals had technical ability and leadership skill, but none on par with Yamamoto; his loss would be a major blow to the Japanese navy’s morale, already reeling from defeats at Midway and Guadalcanal. Layton later described his mixed emotions because he personally knew Yamamoto.
Different sources have different versions of who was involved in making the decision to shoot down Yamamoto. Layton believed it was Nimitz alone. President Roosevelt was out of Washington, DC, during the period and there is no documentary evidence of his involvement. Secretary of the Navy Frank Knox may have been involved as the contents of the message were by then known to a very small circle of people in Washington in office of the CNO, OP-20G, and ONI. Some sources recall a message being sent from Knox to Nimitz, but none has ever been found, nor would it have been standard practice to transmit such a message regarding code-breaking intelligence. The deputy director of ONI, Captain Zacharias, was tasked to write a memo on precedents for killing enemy commanders, but who it was for and where it went is unknown.
Regardless of who else may have been involved, Nimitz made the decision and tasked Vice Admiral William Halsey, commander of U.S. Forces in the South Pacific Area, to plan and execute an operation to shoot down Yamamoto. The task then flowed to Rear Admiral Marc Mitscher, who at that time was Commander, Aircraft, Solomons (COMAIRSOLS), which had superseded the “Cactus Air Force” on Guadalcanal. It was a 400-mile flight from Guadalcanal to Bougainville, and to avoid detection by the Japanese, the outbound leg would have to be a circuitous 600-mile flight. None of the Navy and Marine fighters on Guadalcanal had sufficient range to execute the mission, nor were any aircraft carriers close enough to do so.
The U.S. Army Air Force’s 339th Fighter Squadron, equipped with long-range twin-engine P-38G Lightning fighters was the only force available on Guadalcanal to execute the mission. Even then, special larger 330-gallon drop tanks had to be flown in just in time from General MacArthur’s Southwest Pacific theater in New Guinea. Each fighter would carry one large and one standard drop tank; fortunately, both would be close enough to the aircraft centerline to avoid asymmetric flight problems. Eighteen aircraft and pilots were selected for the mission, including two spares. Four aircraft were designated as the “kill flight,” with the pilots selected by Mitscher due to proven “high-scoring” combat experience. Although the commander of the 339th Squadron, Major John Mitchell, would lead the mission (but was not in the kill flight), a number of the pilots were drawn from two other squadrons because of their experience. At the request of Mitchell, Marine Lieutenant Colonel Luther S. Moore, found and had fitted a U.S. Navy ship’s compass on Mitchell’s P-38 (and possibly in other aircraft as well) to aid navigation.
On 17 April, Halsey approved the plan. The pilots were only told the target was a VIP, and were also told a cover story that the intelligence had been obtained via Australian coast watchers near Rabaul (although it didn’t take long for the pilots to figure out the intelligence came from intercepted communications). When the flight launched, two of the killer flight had to abort (a blown tire and an engine problem) and their designated spares flew in their place. According to the intercepted message, the first leg of Yamamoto’s flight was from Rabaul to an airfield on Balalea Island near Bougainville, and Mitchell calculated the intercept to occur at 0934 local.
Although often described as an inspection tour, a major purpose of Yamamoto in going to Bougainville was to congratulate Japanese naval aviators on what was assessed to be the successful conclusion of Operation I-Go. Operation I-Go was a major Japanese air counter-offensive against Guadalcanal and other locations in New Guinea that commenced on 7 April 1943. The air groups from the carriers Zuikaku and Zuiho (Carrier Division One,) and Junyo and Hiyo (Carrier Division Two) had been flown ashore to airfields in the northern Solomon Islands and near Rabaul. Flying from land bases, the carrier aircraft would participate in strikes with land-based Navy (for Guadalcanal) and Army (for New Guinea) twin-engine bombers. This was no easy feat for the Japanese, since their air groups were not organized or normally equipped to operate independently from their carriers.
On 7 April, the Japanese launched the largest air attack in the Pacific since the attack on Pearl Harbor. Sources vary, but about 70 bombers (including carrier aircraft) and over 110 fighters attacked Guadalcanal. Although Guadalcanal had been relatively calm since the Japanese evacuated in February, there was ample intelligence warning that the raid was coming. U.S. forces around Guadalcanal were at a rare Condition “Very Red,” and 76 U.S. interceptors met the Japanese raid. Given the number of Japanese aircraft involved, the results were unspectacular. Nevertheless, Japanese Val carrier dive bombers from Hiyo’s air group sank the U.S. oiler USS Kanawha (AO-1) and the New Zealand navy corvette HMNZS Moa, which had previously sunk the Japanese submarine I-1. Japanese Vals from Junyo’s battle-experienced air group also struck the destroyer USS Aaron Ward (DD-463) as she was escorting LST-449. Witnessing the attack on Aaron Ward from the LST was Lieutenant (Junior Grade) John F. Kennedy, a passenger on his way to take command of PT-109 at Tulagi. Although Aaron Ward had survived punishing damage during the Friday the 13th Battle (November 1942) off Guadalcanal, the Japanese dive-bomber pilots were apparently some of the best surviving Japanese carrier aviators, and Aaron Ward was hit by several bombs and several damaging near-misses. Aaron Ward sank with 27 of her crew dead or missing and 59 wounded. Her skipper, Lieutenant Commander Frederick Becton survived and went on to command the second USS Laffey (DD-724) during the D-Day landings (where she was hit by a dud German 8-inch shell) and then at Okinawa, where she would survive being hit by about six kamikaze aircraft. Becton would earn a Navy Cross and four Silver Stars during the war, along with two Presidential Unit Citations.
Follow-on Japanese raids on Allied forces on New Guinea met with the same lackluster success, but wildly inflated claims by Japanese pilots convinced Yamamoto and others that I-GO was a big success. It came at a cost of about 55 Japanese aircraft (and about 25 U.S. aircraft) and, not wishing to sustain that rate of loss in his dwindling number of carrier aircraft, Yamamoto declared victory and terminated the operation on 16 April.
Bad omens abounded before Yamamoto commenced his congratulatory tour. Junior staff members tried to convince him not to make the flight, or at least to change the schedule, to no avail. Lieutenant General Hitoshi Imamura, the senior army commander in the Solomons, described how he had narrowly avoided being shot down in the central Solomons a month earlier (this was the same general whose transport had been sunk by Japanese torpedoes aimed at the USS Houston—CA-30—in the Battle of Sunda Strait on 1 March 1942). The commander of the carrier aircraft, Vice Admiral Jisaburo Ozawa (who had relieved Vice Admiral Nagumo after the Battle of Santa Cruz) offered to provide a much larger fighter escort, which Yamamoto declined. The navy staff officer who had “the” message transmitted, was so concerned that Japanese army communications had been compromised that he ordered the message not to be sent via army channels, and then was mortified to learn it had gone out via army communications anyway (and intercepted by the United States, but not decoded to my knowledge). At the last minute, Yamamoto ordered his chief of staff, Vice Admiral Matome Ugaki, to fly in the second aircraft. They had always flown together previously. When both bombers were shot down, Ugaki was one of the three survivors of the aircraft that crashed in the water, despite the fact he was already severely weakened by some jungle disease. Ugaki would go on to command the Japanese battleship group at the battle off Samar at Leyte Gulf in October 1944, and then he would fly what is believed to be the last kamikaze mission of the war (and be shot down), several hours after the Emperor’s surrender announcement. Ugaki’s copious diary would be one of the most valuable documents to survive the war for describing the Japanese side of events.
In the melee that occurred during the intercept, both Japanese bombers were shot down, and although a couple of Zero fighters were claimed, none were actually lost. One U.S. P-38 and its pilot failed to return from the mission, although the exact time and cause of the loss is uncertain. The pilot who the U.S. Air Force would ultimately give credit (many years later) for shooting down Yamamoto’s plane, Captain Rex T. Barber, came back with 104 holes in his aircraft. Captain Thomas G. Lanphier also claimed to have shot Yamamoto down, resulting in a decade-long dispute, and for many years the two shared half credit. When the U.S. Air Force finally sided with Barber, Lanphier lost his “ace” status as he reverted to four kills. The mission was also somewhat marred by security breaches following the mission. The Navy originally submitted the mission commander, Major Mitchell, for a Medal of Honor, but this was downgraded to a Navy Cross prior to approval because the Navy was so incensed by the “loose talk” of the pilots. However, all pilots who flew the mission were awarded Navy Crosses.
The Japanese did not announce Yamamoto’s death until 21 May, although U.S. Navy communications-traffic analysts and cryptanalysts were able to determine by changes in Japanese communications that he had been killed almost immediately. Yamamoto’s death was a major blow to Japanese navy morale, having much the effect that Eddie Layton had predicted. Like Layton, a number of the intelligence personnel involved in the operation would later express mixed feelings. Whether they had met Yamamoto personally or not, through their intelligence analysis they had come to know Yamamoto as a respected and worthy adversary. It also turned out long after the fact that the code breakers had been incorrect: Yamamoto’s first destination was apparently Buin and not Balalea airfield, but it proved to be “close enough.”
(Sources include: Combined Fleet Decoded: The Secret History of American Intelligence and the Japanese Navy in World War II by John Prados, as well as And I Was There: Pearl Harbor and Midway—Breaking the Secrets by Edwin Layton and Roger Pineau; and Double-Edged Secrets by Jasper Holmes, as well as Samuel Eliot Morison’s History of U.S. Naval Operations in World War II series.)
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