Alva Bryan Lasswell
Colonel (USMC)(Retired)
January 3, 1905 – October 28, 1988)
by Tom Hunnicutt

Colonel Alva Bryan Lasswell was born on January 3, 1905 in Walpole, Illinois, but spent most of his youth in Clay County, Arkansas after his family moved to the town of Piggott. He attended high school in Clay County, but failed to graduate. For the most part he was home-schooled by his father, Charles S. Lasswell, who was a school teacher, farmer and lawyer. At the age of thirteen Lasswell tried to join the Marine Corps, but was too young. He moved to Oklahoma in 1921, working as an accountant for a few years, but his desire to join the Marine Corps continued. In the fall of 1925, still a few months short of twenty-one, he was finally able to enlist.

Lasswell was recommended for the 1928/29 Officer’s Candidate School and was commissioned a 2nd Lieutenant on January 30, 1929. By early 1935, then Lieutenant Lasswell was enrolled in the foreign language training program and was sent to Japan to study Japanese, where he remained until 1938.

International Community - Shanghai

Colonel Lasswell’s first significant effort in Communications Intelligence came in July of 1940 when, as a Captain, he was assigned to the 4th Marine Regiment in China for duty as the Officer-in-Charge (OIC) of Radio Station “A” in Shanghai, China. His cryptanalytic skill with Japanese diplomatic codes and his knowledge of the Japanese language enabled him to decrypt and translate a Japanese plot to impose martial law on the international community of Shanghai. This information allowed the Commander of the 4th Marine Regiment, in Shanghai to protect American interests there, to adopt a plan that was ultimately successful in preventing the Japanese efforts to install martial law on the international community.

World War II

Prior to, and during, the Pacific campaigns of World War II there was a little known unit, affectionately known to a few as “The Dungeon”. In early 1941 then Captain Lasswell was on his way to the Territory of Hawaii to head the Language Training Center at the University of Hawaii. Instead, he found himself assigned as Chief Translator in the Communication Intelligence Unit in Fleet Radio Unit, Pacific (FRUPac). That unit was headed by then Commander Joseph J. Rochefort (who was inducted into NSA’s Hall of Honor in 2000). Commander Rochefort had requested Captain Lasswell, by name, because of Lasswell’s reputation as a skilled cryptolinguist. Captain, soon to be Major and later Lieutenant Colonel, Lasswell, was one of ten officers and thirty enlisted personnel assigned to the “Dungeon”. Only two of the officers were both cryptanalysts and Japanese linguists; Captain Lasswell and Lieutenant Commander Joseph Finnegan.

The significance of this unit and the men who staffed it is reflected in a December 8, 1945, narrative report by Captain C. H. McMorris, the Pacific Fleet, Chief of Staff. On pages 3 and 4 of that report he stated: “The fate of the nation quite literally depended on about a dozen men who had devoted their lives and their careers, in peace and war, to radio intelligence.” Eight of these men worked in the basement of the Administration Building at Naval Headquarters, Pearl Harbor, in a space called ”The Dungeon”. “Seven were naval officers and one was a Marine officer … … The officer-in-Charge was Commander J. J. Rochefort … … without (whose) inspiring leadership, technical competence, unselfish devotion to duty and his personal example of untiring effort, it is doubtful that the full result could have been achieved. … … it is devoutly to be wished that the nation will never be so poor but that men will be found to make similar sacrifices.”

The National Security Agency (NSA) Hall of Honor 2000 Inductee article states the following concerning Captain Joseph J. Rochefort, USN: “The most significant cryptologic success was the timely accurate support by Rochefort and his unit surrounding the Battle of Midway, considered by many to be the turning point of the war in the Pacific. Station Hypo (Wahiawa/FRUPac) provided accurate and timely intelligence reports for the rest of the Pacific War; these reports were used by the most senior navy officers for strategic and tactical decisions”.

Upon his arrival at FRUPac, Captain Lasswell was tasked by Commander Rochefort with the responsibility for setting up the operations. Lasswell set up a twenty-four hour on, twenty-four off watch schedule. Captain Lasswell remained at FRUPac until October 1944, followed by assignment to NAGET (Washington, DC’s counterpart to FRUPac) in the same billet until October 1945.

Battle of Midway

Prior to the Battle of Midway, each member of “The Dungeon” worked on incoming Japanese messages in varying degrees. However, Lasswell and Finnegan, being the most experienced, did most of the recoveries on the Japanese Code JN-25. Lasswell wrote in his memoirs that prior to the attack on Pearl Harbor the work was painfully boring for they received little to no traffic to work on. However, after the war broke out they started receiving more traffic, which led to longer hours in “The Dungeon”, but the work was rewarding. It required total dedication and it was at this time that their cryptanalytic and translating skills paid off. Lasswell’s efforts stood out above the others for it became a passion with him and he pushed himself hard to achieve good results. At times he slept near his desk and, after gaining a little rest, pushed himself harder to achieve superior results. As a result, he became the key translator for FRUPac in the 1942-1944 period, during which invaluable intelligence was acquired.

On one particular night, as Lasswell scanned through the messages waiting to be worked on, he noticed a very unusual one. It turned out to be a Japanese Navy Operation Order. He worked on it all night and by 0800 the next morning he sent it out to all major fleet commands. The order identified a major Japanese attack in the offing, however, there was a difference of opinion between FRUPac and NEGAT as to the target of that attack. Lasswell believed that the Japanese code group for the target, “AF”, was Midway Island, while NEGAT believed it to be Hawaii. Admiral Chester W. Nimitz, Commander-in-Chief, Pacific Fleet, made a personal visit to “The Dungeon” to ask Lasswell how sure he was of the target location. Lasswell told him he was one hundred percent sure. In order to verify the target Commander Rochefort and another officer developed a scheme to verify the location of the suspected attack. They came up with an idea of sending a fake message out from the Midway Defense Command, unencrypted, stating that they had a problem at the Midway water desalinization plant. The next day Navy intercept operators copied a Japanese message that, when translated, stated that “AF” was having problems with their water system, thus verifying Midway as the Japanese objective. Knowing the Japanese target enabled the U.S. Navy to deliver a devastating blow to the Japanese fleet and, almost without exception, military historians consider this information to have been invaluable and the battle itself to have turned the tide of the war in the Pacific theater.

Shootdown of Admiral Isoroku Yamamoto

On April 13, 1943, LtCol Lasswell decoded and translated another Japanese naval message that became part of naval history. That message was intended to inform an outpost of the planned visit of Admiral Isoroku Yamamoto, who would be flying from the Japanese-held island of Rabaul to the Island of Bougainville. The message gave details of his escort fighters and the exact time of his arrival. With this information, Admiral Nimitz began planning an attack on Yamamoto’s aircraft. The attack took place on April 18, 1943, the first anniversary of the Doolittle Raid on Tokyo. The Army Air Corps is credited with the actual shoot down of Admiral Yamamoto’s aircraft.

The shoot down of Admiral Yamamoto was also addressed by Captain McMorris in his narrative report, which includes a unique reference giving credit to LtCol Lasswell for the decryption/translation of the message leading to the shootdown. In that narrative McMorris stated: “The Yamamoto story is illustrative of the danger in operational use of radio intelligence. When the message which led to the successful interception of Admiral Yamamoto was broken (by Lieutenant Colonel Lasswell, USMC), he instantly recognized the dangers involved in this use. Every fully indoctrinated officer who handled the material was likewise aware of the potential danger.” Colonel Lasswell was again the key figure in the intelligence analysis and translation that resulted in another devastating blow to the Japanese, not just the loss of one of Japan’s greatest military minds, but also to the morale of the Japanese military.

Plot to Ambush General MacArthur

A plot was formed by the Japanese to ambush General Douglas MacArthur when he returned to the Philippines. The Japanese Navy ordered seven of their submarines to take up positions around the east coast of New Guinea. They were placed into the exact position, seven miles apart, along the route they expected MacArthur would take in his return to the Philippines. Although the date is not indicated, this took place between July or early September 1944 while Colonel Lasswell laws still assigned as Chief Translator at FRUPac. It is believed the Japanese wanted to eliminate MacArthur as payback for the death of Admiral Yamamoto in 1943, thus giving a great morale boost to the struggling Japanese troops throughout the entire Pacific. MacArthur returned to the Philippines in October 1944 and, according to Lasswell, all seven of those Japanese submarines were destroyed by Navy ships and submarines.

Another source of information regarding this incident advised that in May of 1944, a Japanese submarine commander’s radio operation order was intercepted and partially decrypted. Subsequent plotting and additional decryption yielded fairly reliable information on the position of the patrol line to be established by the operation order. That information was made available in sufficient time to have a carrier antisubmarine group ordered out to operate against the patrol. This report stated that the USS England sank five of the seven submarines involved.

While there are two different stories about the same incident, we do know that Colonel Lasswell was still at FRUPac at this time and during an interview by Mr. R. D. Farley from the National Security Agency (NSA), he remembered enough detail to give his account of events credibility.

Mouse Trapping

These three incidents and results speak for themselves, but there were other major Japanese Battle Plans broken and translated that dealt with a wider range of military operation during those days. It was called, Mouse Trapping, a term used by operational commanders to formulate their tactical battle plans. By jumping over islands of little importance, they cut off the enemy on those islands, to nbe mopped up at a later date. The stranded Japanese forces had no means to leave or cause trouble, which saved both lives and time, as the Pacific campaign moved forward. According to Mr. R. D. Farley from NSA, Lasswell also recovered and translated many of these messages, which led to various island assaults. In a letter dated September 2, 1943, recommending that Lieutenant Colonel Lasswell be promoted to Colonel, Admiral Nimitz stated that he “… contributed materially toward the successful conclusion of the Battles of the Coral Sea, Midway and the Solomons…”


Many of us in the Marine Corps Cryptologic Association, and especially on its Board of Directors, are veterans of both the Cold War (Soviet Union) and a Hot War (Vietnam), with either formal training in, or a working knowledge of, the fields of cryptanalysis and linguistics. When the exploits of Colonel Alva Bryan Lasswell are considered by us, it is difficult not to see how incredibly important he was to the war effort and how much his skills in cryptanalysis and the Japanese language impacted on the early successes enjoyed by the United States forces, especially the Navy, in the Pacific Theater of Operations.