Outside the Box: Naval Radio Intercept Intelligence December 25, 1941 – June 7, 1942
By: Jonathan Wanzer ORCiD 0009-0004-9275-7410
Submitted on: August 8, 2022
Submitted to: Dr. Allen York – Liberty University
Course: HIWD 555 World War II
Chicago Citation:
Wanzer, Jonathan. “Outside the Box: Naval Radio Intercept Intelligence December 25, 1941 – June 7, 1942.” Historical Interpretations. Jonathan Wanzer, August 8, 2022. http://wanzer.org/outside-the-box-naval-radio-intercept-intelligence/.
Introduction
Admiral Chester Nimitz arrived at his new command at Peral Harbor the morning of December 25th, 1941. The events of the next five years are the subjects of numerous books and movies. An important detail often not covered in these recountings and dramatizations is the crucial relationship between command and intelligence under Nimitz. Nimitz had an uncommon relationship with the intelligence gathering units under his command. It is this close connection to locally processed signals intelligence that gave the outnumbered U.S. Pacific Fleet an advantage over the Japanese Navy eventually allowing the U.S. to significantly deplete the Japanese fleet, crush their commercial shipping, and hold the war in the Pacific to an ever-tightening perimeter around Japan until the end of the war.
This special relationship between command and the intelligence unit in Hawaii was proven effective in the events leading up to the Battle of the Coral Sea, the attack on Dutch Harbor, and the Battle of Midway.
Coral Sea
While intelligence operations were conducted locally with the intercepts that were forwarded to Washington for analysis and interpretation, the products returned to the theater were often of a lower standard than that originated from the unit at Peral Harbor. The following excerpt of a letter[1] from a Navy cryptologist serving at Peral Harbor from 1943 to 1945 shows the high level of skill provided by the local intelligence team:
Our routines were more informal than many in the Navy. For example, I remember Stanley Moe, a yeoman, who was an expert in reading enemy weather traffic. He would start analyzing the new intercepts promptly after 00:00 minus nine time and would often have everything figured out in a couple of hours. He, Kenny Lee, and I worked together around the clock for three or four days to break a new daily-changing call sign encipherment system, with the familiar weather intercepts providing the raw material for the reconstruction on what turned out to be a very simple strip cipher. I remember the incident with particular pleasure because several days after we had the whole thing figured out, we were still getting messages from Washington advising us they had recovered a few values.
Admiral Nimitz Intelligence Officer, Lieutenant Commander Edwin Layton had a long-standing relationship with the Japanese-Language Officer at Intelligence Station in Hawaii, Hypo, Joe Rochefort who was knowledgeable in the Japanese language, and had studied the culture of the Japanese. He was in a position to go well beyond a simple translation.[2] Rochefort continued to send his translation and interpretations to Washington along with the daily intelligence intercepts and reports, where they were analyzed by people without his compliment of skills and often disagreed with his conclusions or simply felt there was not enough content to substantiate his interpretations. John Stevens recounted “I prepared the report on the previous 24 hours of intercepted traffic that was sent to Commander Layton at CINPAC the first thing in the morning.”[3] Stevens and Rochefort provided Layton with intelligence that was actionable right from Hypo.
Fortunately, Layton knew Rochefort’s skills and trusted his interpretations. Layton would take Rochefort’s reports directly to Nimitz. Eventually, the Washington processed version of the reports would make their way to Nimitz often missing information or having different conclusions. This situation demonstrates not only the need for properly skilled interpreters of intelligence, it also demonstrates the need to have that interpretation readily available to command. This bares out in the intercepts indicating that the Japanese were planning to attack Australia and would be transiting the Coral Sea.
Thanks to the Hypo teams focus on Japanese fleet and vessel movement after the attack on Peral Harbor, in April 1942 they began to see messages indicating an invasion force and what they knew was the two-letter code for Port Moresby. With the continuing intelligence, plans were made to anticipate the Japanese attack and arrive in the Coral Sea ahead of the Japanese attack force to cut them off in a surprise counter offensive. As planning progresses, Rochefort’s team began to narrow the timeframe and the carriers that would be involved in the attack. Rochefort’s superior in Washington, Captain John Redman, didn’t have confidence in the Hypo assessment and believed the plan was actually an attack on the Aleutian Islands.[4]
Fortunately, Nimitz was inclined to believe Rochefort’s interpretation of the interceptions and planned accordingly. The Hypo interpretation would prove to be correct with the details of ships involved, their locations, and the timing of their arrival being close to what was expected from the decoded intercepts.
Dutch Harbor
After the battle of the Coral Sea Nimitz confidence in the Hypo teams abilities to provide timely and accurate intelligence was clearly justified.[5] Intercepts continued to come in and the team was rapidly improving their ability to decode, interpret accurately, and more quickly.
Washington was sure the Japanese were planning to attack the Aleutian Islands of Alaska and that the intercepts indicated that attack on Midway was a diversion. Rochefort believed that Midway was the target, and initially Dutch Harbor was a diversion.[6] Later he would believe this attack was just another target and not tactically connected to Midway.
Midway
Midway was clearly the primary target for the Japanese Fleet in 1942. In a briefing on May 10th Layton reported that the Japanese were amassing a battle group of two to four carriers. Rochefort believed the target to be Midway. This information dramatically changed Nimitz plans for rehabilitating his own carriers, it also informed Nimitz tactics in preparation for the coming attack. Nimitz needed the pacific fleet nimble and at full capabilities.
In the morning briefing of May 15th Layton presented Rochefort’s findings that the target of the next attack was Midway with the increase in radio traffic including the target AF, Midway. At the same time Admiral King was insisting that Midway was only one of half a dozen other targets in the Pacific based on intelligence from Washington. King was also informed by London that the British did not have any intelligence indicating any mid-Pacific targets.[7] In a brilliant tactic, Nimitz had Admiral Halsey expose his carrier group in the Coral Sea. This acted as a counterintelligence move confirming that the Japanese knew his position which prevented attacks around the Coral Sea, and it gave Nimitz the reason he needed to recall Halsey to Peral Harbor to resupply and prepare to redeploy to the Northeast of Midway.[8]
Conclusion
The signals intercept interpretation issues felt in the Pacific from 1939-1945 were also being scrutinized at both the Department of Naval Intelligence and the competing Office of Naval Intelligence. The conflicts began heating up after Peral Harbor, by the time the regional conflict regarding the interpretation of Dutch Harbor and Midway intercepts were clarified there were many concerns about the future of Naval Intelligence.[9] While the DNI and ONI conflict and the future of naval intelligence is outside the parameters of this paper, it is important to recognize that the close relationship of intelligence and command was noticed in circles outside of operations, and the Nimitz, Rochefort connection played a role in the eventual overhaul of Naval Intelligence.
The superiority of American Naval intelligence in the Pacific was aided considerably by the Japanese relatively weak intelligence due to misconceptions and an unwillingness to make corrections.[10] Where U.S. Naval intelligence excelled was in the close out of the box relationship in Admiral Nimitz command. Maintaining a clear and short path for intelligence to reach command when needed requires a strategic culture, an ongoing and cultivated process, developed through “a habit of behavior”[11] within the working intelligence group informed by a consistent set of beliefs centered around the policies of force, the applications of that force, and how it meets challenges.[12]
Bibliography
Borneman, Walter R. The Admirals: Nimitz, Halsey, Leahy, and King: The Five-Star Admirals Who Won the War at Sea. New York, NY: Back Bay Books, 2013.
Dorwart, Jeffery M. Dorwart’s History of the Office of Naval Intelligence, 1865-1945. Annapolis, MD: Naval Institute Press, 2019.
Ford, Douglas. “Strategic Culture, Intelligence Assessment, and the Conduct of the Pacific War: The British-Indian and Imperial Japanese Armies in Comparison, 1941-1945.” War in History 14, no. 1 (2007): 63-95
Gray, Colin S. Modern Strategy. New York, NY: Oxford University Press, 1999.
Naval Cryptologic Veterans Association (U.S.). U.S. Navy and Marine Corps WWII Cryptologists’ Oral Histories: Voices from the Past. Vol. 1. 2 vols. Pensacola, FL: US Naval Cryptologic Veterans Association, 2019.
Naval Cryptologic eterans Association (U.S.). U.S. Navy and Marine Corps WWII Cryptologists’ Oral Histories: Voices from the Past. Vol.2. 2vols. Pensacola, FL: US Naval Cryptologic Veterans Association, 2019.
Symonds, Craig Lee. The Battle of Midway. New York, N.Y: Oxford University Press, 2011.
Symonds, Craig L. Nimitz at War: Command Leadership from Pearl Harbor to Tokyo Bay. New York, NY: Oxford University Press, 2022.
[1] John Paul Stevens, U.S. Supreme Court Justice to Charlie Walters, executive Director, U.S. Naval Cryptologic Veterans Association. 22 February 1995. In response to a request for a “page or two” on his service in the Navy in WWII. Paragraph 4. Naval Cryptologic Veterans Association (U.S.). U.S. Navy and Marine Corps WWII Cryptologists’ Oral Histories: Voices from the Past. Vol. 2. 2 vols. Pensacola, FL: US Naval Cryptologic Veterans Association, 2019. 271.
[2] Craig Lee Symonds, The Battle of Midway, New York, N.Y: Oxford University Press, 2011. 133-152
[3] John Paul Stevens to Charlie Walters, paragraph 3. U.S. Navy and Marine Corps WWII Cryptologists’ Oral Histories: Voices from the Past, vol. 2. 2 vols., 270.
[4] Craig Lee Symonds, The Battle of Midway, 2011. 146-7
[5] Craig Lee Symonds, Nimitz at War: Command Leadership from Pearl Harbor to Tokyo Bay, New York, NY: Oxford University Press, 2022. 107-10.
[6] Craig Lee Symonds, The Battle of Midway, 2011. 198-200
[7] Craig Lee Symonds, Nimitz at War, 2022. 100-1
[8] Craig Lee Symonds, Nimitz at War, 2022. 100-1
[9] Jeffery M. Dorwart, Dorwart’s History of the Office of Naval Intelligence, 1865-1945, Annapolis, MD: Naval Institute Press, 2019. 283-4
[10] Douglas Ford, “Strategic Culture, Intelligence Assessment, and the Conduct of the Pacific War: The British-Indian and Imperial Japanese Armies in Comparison, 1941–1945,” War in History 14, no. 1 (2007): 63–95, 64.
[11] Colin S. Gray, Modern Strategy, New York, NY: Oxford University Press, 1999. 138.
[12] Douglas Ford, War in History 14, no. 1 (2007): 63–95, 64.