The Japanese surprise attack on Pearl Harbor in December 1941 was a very complex operation that required precise information about the movement and disposition of the US Pacific Fleet, based at Hawaii. This information was gathered on the ground by a spy named Takeo Yoshikawa, who cabled regular reports to Tokyo. These reports proved to be invaluable to the success of the Japanese attack. However, this constant supply of information almost gave the game away.
Here, Alan Bardos, author of a related novel: Amazon US | Amazon UK, considers whether the attack on Pearl Harbor could have been avoided.
During the attack on Pearl Harbor, the West Virginia was sunk by six torpedoes and two bombs.
Our Man in Hawaii
The US Pacific Fleet moved from its bases on the West Coast of America to Pearl Harbor in 1940, so the Japanese consequently had very little information about it. The sailing of their fleet over 3,500 miles from home waters to Hawaii was a massive undertaking that required their ships to be refueled numerous times en route. Before taking such a risk they therefore needed to know what was waiting for them when they arrived and the best time to attack.
Bureau 3 (Intelligence) of the Imperial Japanese Navy’s General Staff attached Takeo Yoshikawa to the Japanese Consulate-General in Honolulu. His mission was to gather news about Pearl Harbor. His orders were vague and were constantly refined by further instructions from his superiors in Tokyo.
Yoshikawa meticulously gathered vital intelligence on the movements of the US Pacific Fleet and Hawaii’s defenses. He spent his days travelling between various observation points around Hawaii, reconnoitering airfields and the US Fleet. Changing his clothes several times through the course of the day, he would blend in as anyone from a tourist to a Filipino-American laborer. Yoshikawa even took geisha girls as cover on sightseeing flights over Pearl Harbor. Postcards he supplied were found in the cockpits of Japanese aircraft shot down over Pearl Harbor. Crucially, Yoshikawa was said to have discovered that Sunday mornings were the best time to attack, when the Fleet was home from maneuvers.
Yoshikawa communicated this information regularly to Tokyo through commercial American telegraph companies. In the run up to the attack Tokyo’s need for information increased steadily, to the extent that Yoshikawa was reporting the US Fleet’s movements on a daily basis, leaving a large paper trail of his activities.
The number of cables sent by the Japanese Consulate hadn’t gone unnoticed and Robert L. Shivers, the FBI’s Special Agent In Charge in Hawaii tried to persuade the cable companies to share the coded messages with him but they refused, not wishing to break Federal Law.
Magic intercepts
American Intelligence had broken the Japanese diplomatic codes and were regularly intercepting and decrypting Japanese diplomatic traffic, as part of a program code named Magic. This used a machine code named Purple to decode these messages, which were then translated manually. The Americans were therefore aware that war was coming in the Pacific, but only knew as much as Japan’s diplomats, who were not informed in any detail of their Military’s plans. The US Army and Navy Departments in Washington did issue war warnings to their Pacific commanders, but the warnings were consequently vague and did not suggest that Hawaii would be a target.
Faced with an overwhelming amount of decrypted information, American Intelligence focused their efforts on translating the high level communications between Tokyo and the Japanese Embassy in Washington, which was conducting peace talks with the American government. This did eventually provide a warning of a coming attack, but it did not say where it would be.
Dorothy Edgers and the deferred intercepts
Yoshikawa’s telegram’s to Tokyo gave precisely this information, but as Hawaii was considered a diplomatic backwater, they were left untranslated in the “deferred” pile until one bored newbie in the Naval Cryptographic Section decided to look at them.
Mrs. Dorothy Edgers, a former school teacher in Japan, had been working as a translator for two weeks when she found herself in the office on a Saturday morning. She had nothing to do, but was eager to be involved in this strange new world of signals intelligence and started to translate the Hawaii decrypts.
She struck gold immediately realizing the importance of the correspondence between Yoshikawa and Tokyo. Enwrapped, Mrs. Edgers translated telegram after telegram that gave away the military secrets of her country, from real time movements of its battleships, to the lack of torpedo nets protecting them, to the position of the airfields tasked with defending them. This was clearly more than the routine reports of a sidelined diplomat in a backwater, but information for a full-scale attack.
Mrs. Edgers reported her findings to her immediate supervisor Chief Ship’s Clerk Bryant. He saw their significance, but it was Saturday and they were finishing at 12:00pm so he told her it would wait until next week.
Not put off, Dorothy Edgers continued to translate the decrypted messages, waiting in the office for the return of the Translation Branch chief, Captain Alvin Kramer, who had been making his rounds delivering the latest high priority Magic Intercepts. Mrs. Edgers briefed Kramer on what she’d found and was reprimanded for her trouble.
Tired and with a number of other conflicting priorities, Kramer was annoyed that she worked late after the office had closed and was unhappy about the quality of her translation. He dismissed her in no uncertain terms and she was told once again that it would wait until next week.
Ordinarily, Bryant and Kramer would have been right, but on this occasion it was the day before the Pearl Harbor attack.
December 7th 1941 - A date that will live in infamy
The next day, on reviewing the priority daily intercepts between Tokyo and their Embassy in Washington, Kramer saw things were clearly coming to a head. Tokyo had instructed its delegation to end their negotiations at 1pm precisely.
Kramer had been stationed in Hawaii and knew that 1pm in Washington was dawn in Hawaii, and worked out what time 1pm would be at all the US bases in the Pacific, with it being a few hours before dawn in the Philippines.
He passed his findings onto Commander McCollum and Captain Wilkinson, his superiors in the Office of Naval Intelligence. They took them to Admiral Stark the Chief of Naval Operations, who was not overly impressed, but after further discussion and consulting with General Marshall, his opposite number in the Army, Stark agreed to issue an alert to his bases in the Pacific. However, due to atmospheric conditions, they were unable to send the warning to Hawaii and it was sent as a low priority telegram and arrived just after the attack had finished.
They believed that the main threat they were facing was an amphibious landing in the Philippines, where it would be the optimum time for that type of attack and there were also reports of Japanese ships moving in that direction. Had Yoshikawa’s reports been more widely distributed, a very different conclusion might have been reached.
Admiral Kimmel, the Commander in Chief of the Pacific Fleet and the man blamed for the attack categorically argued that had he been aware of the Hawaiian decrypts, he would have been better prepared to counter the surprise attack. That was certainly the findings of a subsequent congressional investigation.
Many of the events depicted in this article inspired my novel ‘Rising Tide’, which can be purchased here: Amazon US | Amazon UK
Book full name: Rising Tide (Daniel Nichols Spy Thrillers Book 1) eBook : Bardos, Alan : Kindle Store
References
Japan's Spy at Pearl Harbor: Memoir of an Imperial Navy Secret Agent, Takeo Yoshikawa, McFarland (2 Mar. 2020).
The Broken Seal: "Operation Magic" and the Secret Road to Pearl Harbor, Ladislas Farago, Westholme Publishing; Reprint edition (25 Oct. 2012).
A Matter of Honor: Pearl Harbor: Betrayal, Blame, and a Family's Quest for Justice, by Anthony Summers and Robbyn Swan, Harper; Reprint edition (15 Nov. 2016).
Countdown to Pearl Harbor: The Twelve Days to the Attack, by Steve Twomey, Simon & Schuster; Illustrated edition (1 Nov. 2016).
Pearl Harbor: From Infamy to Greatness, by Craig Nelson, Weidenfeld & Nicolson; 1st Edition (10 Nov. 2016).
https://www.usni.org/magazines/proceedings/1960/december/top-secret-assignment
