The Secret Sentry by Matthew M. Aid Read Free Book Online Page A

the Pusan Perimeter. For example, an intercept revealed that ammunition shortages in the North Korean
Thirteenth Division east of Taegu were so severe that it could not fire its few remaining artillery pieces. 11
    The Inchon Landing
    In one of the greatest gambles of the Korean War, on the morning of September 15, 1950, units of the U.S. Tenth Corps staged
an amphibious landing, planned by General MacArthur, behind the North Korean lines at the port of Inchon, west of Seoul.
    Recently declassified documents reveal that the Inchon landing would not have been successful without the SIGINT coming out
of AFSA. Thanks to SIGINT, MacArthur and his intelligence chief, Major General Charles Willoughby, had a fairly clear picture
of the North Korean army order of battle, including the locations, strengths, and equipment levels for all thirteen infantry
divisions and a single armored division deployed around the Pusan Perimeter. Most important, the SIGINT data showed that there
were no large North Korean units deployed in the Inchon area. 12 In the month prior to the Inchon landing, MacArthur’s intelligence analysts in Tokyo, thanks to the decrypts, were able to
track the locations and movements of virtually every unit in the North Korean army. In mid-August, SIGINT revealed that the
North Koreans were taking frontline combat units from the Pusan Perimeter and moving them to defensive positions along both
the east and west coasts of South Korea, suggesting that the North Korean general staff was concerned about the possibility
of a U.N. amphibious landing behind North Korean lines. By early September, decrypted high-level North Korean communications
traffic showed that the North Korean army’s senior commanders were concerned that the United States might attempt an amphibious
landing on the west coast of South Korea, but had incorrectly guessed that the landing would most likely occur to the south
of Inchon at either Mokpo or Kunsan port. 13
    Despite SIGINT indications that the North Koreans knew a U.S. amphibious operation was imminent, MacArthur went ahead with
the landing at In-chon on September 15. It was a stunning success, with little North Korean resistance. The sole attempt by
the North Koreans to mount a major counterattack against the Inchon bridgehead was picked up by SIGINT well before it began,
and mauled by repeated air strikes. In a matter of just a few hours, the entire North Korean force was destroyed. 14
    With the collapse of the Inchon counterattack, there were no more organized North Korean forcesstanding between the U.S. forces
and Seoul. On September 28, Seoul fell to the Americans. With that, all thirteen North Korean combat divisions around the
Pusan Perimeter abandoned their positions and fled to the north. By the end of the month, all of the rest of South Korea up
to the old demarcation line at the 38th parallel had been recaptured.
    The Chinese Intervention
    Newly declassified documents have revealed that at the time of the Inchon landing, AFSA had very few SIGINT resources dedicated
to monitoring what was occurring inside the People’s Republic of China, North Korea’s huge communist neighbor, because, as
a declassified NSA history put it, AFSA had “employed all available resources against the Soviet target.” The only SIGINT
resources available were a few intercept positions at the U.S. Army listening post on the island of Okinawa, Japan, which
were monitoring low-level Chinese civil communications traffic, primarily unencrypted Chinese government cables and the communications
traffic of the Chinese Railroad Ministry. A small team of Chinese linguists at Arlington Hall Station, headed by a twenty-nine-year-old
New Yorker named Milton Zaslow, was able to derive a modicum of intelligence about the state of the Chinese economy, transportation
and logistics issues, and even the movements of Chinese military units inside China from these telegrams. It was not a very
impressive effort, but it was all that