Letter from Lt. John Leitweiler, Commander of Station CAST, Corregidor to Lt. Lee W. Parke, Chief, Japanese Cryptography Section, U.S. Navy November 16, 1941: Page 1, Page 2

Commentary by Robert B. Stinnett:

This letter (retrieved from the U.S. Navy Archives II, May 16, 2000) directly contradicts one of the official Pearl Harbor media cover stories. Written by Lieutenant John Lietwiler, commanding officer of Station CAST, the U.S. Navy’s monitor facility on Corregidor, in the Philippines, the letter is one of Pearl Harbor’s major “smoking guns.” Addressed to Lieutenant L. W. Parke, head of the Japanese crypto section in the Navy Department, Washington, D.C., it discloses that U.S. naval cryptographers were “current” in intercepting, decoding, and translating Japan’s main operations code as of November 16, 1941 (Manila time).

An exasperated Lietwiler goes further and suggests Parke stalled decrypting Japan’s principal naval code used in the fall of 1941. “I certainly wish you could see your way clear to drop the ancient history side of this cipher and work with us on the current system . . .,” writes Lietwiler. Apparently, Parke directed that Lietwiler’s cryptographers engage in solving expired Japanese naval codes, not the current system used by Japan’s admirals in the fall of 1941, to organize the Pearl Harbor attack.

The letter was secreted from all investigations of Pearl Harbor including both Congressional inquiries of 1945-46 and 1995. Its concealment gave rise to the media cover story that the U.S. did not break Japan’s navy code until after Pearl Harbor.

In June 1941, Station CAST was directed to solve the major Japanese naval code as their principal crypto assignment. The order came direct from the U.S. Chief of Naval Operations, Admiral Harold Stark. To aid in solving the code, Stark’s assistant, Rear Admiral Royal Ingersoll, approved the construction of a decrypting device and dispatched one of the U.S. Navy’s top code breakers to take command of CAST. The task: solve the code which Japan’s naval chief designated Code Book D, Random Number Table 6. The U.S. Navy’s designator for the code was called the Five Number Code, sometimes AN-1 Code. The code was structured around five numbers that stood for a Japanese word or phrase.

In 1941, a multitude of five number groups formed the basic code book. Japan’s designator for the system was Ango-sho D (Code Book D). Then to provide the code with extra security, Japan devised a set of random numbers that used adding and subtracting components as a further encipherment. These random numbers were changed about every five months in 1941. From February to July, the random number component was designated Table 6 (Ransuhyo Ippan Roku). From August to December 4, Table 7. The Japanese designator is shown on each radio dispatch, according to Japan’s military archives in Tokyo.

The Imperial Navy’s code was a top priority for the U.S. Navy’s cryptographers. Code Book D, Table 7 was used by Japan’s admirals and commanders to secretly organize the Pearl Harbor attack and invasions of Southeast Asia. Japan’s admirals believed their code was unbreakable and totally safe to use. U.S. cryptographers could intercept, solve, and translate the code, then President Franklin D. Roosevelt and his administration would know all of the Imperial Navy’s strategy and tactics in advance.

To accomplish this end, Admiral Ingersoll moved Lieutenant John Lietwiler from the Washington, D.C. Crypto center to CAST, along with the special decrypting device. Lietwiler’s orders: solve Code Book D. Both arrived. Both arrived on Corregidor in September 1941. The device was masked in secrecy and called JEEP IV. It was invented by the U.S. Navy’s military cryptographic section chief, Lieutenant Lee W. Parke for the sole purpose of solving the random number components of Code Book D. Lietwiler and JEEP IV went right to work. First, Lietwiler assumed command from outgoing CAST commander, Lieutenant Rudolph Fabian, who was slated for transfer to the U.S. mainland.

By November 16, 1941 (Manila time), Lietwiler informed Parke that he was “reading enough current traffic to keep two translators very busy.” He wrote that JEEP IV was seldom used in decrypting for a member of his crypto staff could “walk right across” the number columns that concealed the words of Code Book D. Lietwiler’s frank comments indicate a possible personal rift with Parke. In his first two words, Lietwiler informs Parke that his invention was a “novelty” and seldom is in use. It is highly unusual for naval officers to engage is such rhetoric in official communications.

In paragraph three, Lietwiler politely suggests Parke attempted to derail CAST’s efforts to decrypt Table 7, Japan’s Pearl Harbor code system. Apparently, Parke wanted CAST to concentrate on the outdated Table 6 that was in effect from February 1 to July 31, 1941. Lietwiler refused: “We stopped work on the period 1 February 1 to 31 July as we have all we can do to keep up with the current period,“ (Table 7). These are strong words from CAST’s commander. In effect, he wished Parke would “see your way clear to drop the ancient history side of this cipher (referring to Table 6) and work with us on each current system (Table 7).”

The Lietwiler-Parke exchange raises major historical questions. Why would Washington officials want to stall CAST’s decryption of the current edition of Japanese naval code in mid-November 1941? Was it to keep Japan’s Southeast Asia and Pearl Harbor strategy from the U.S. Pacific military commanders?

In the upper right corner of the letter, a routing designator indicates the letter was seen and initialed by Captain Laurance F. Safford (LFS), the commander of the U.S. Navy’s communications intelligence division. Military records in Archives II indicates Safford asserted that the United States was reading 90% of Japan’s naval code prior to December 7, 1941. During his testimony to Congress and other Pearl Harbor investigations, Safford never referred to this letter nor was it introduced into evidence.

Footnote: Lietwiler, who was affectionately known to his staff as “Honest John,” never made it to the U.S. Navy’s big time. However, Parke did. Later in the war years, Parke was promoted to Captain and headed the U.S. State Department’s worldwide encryption efforts. Lietwiler remained in the navy’s backwaters and although scheduled as a witness, never was called to testify before any of the Pearl Harbor inquiries. He died in 1978.

View Letter from Lt. John Leitweiler, Commander of Station CAST, Corregidor to Lt. Lee W. Parke, Chief, Japanese Cryptography Section, U.S. Navy November 16, 1941: Page 1, Page 2