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

completed on July 3, the same day that the port of Inchon fell to the North Koreans. A quick scan of the intercepts revealed
that the North Korean army was transmitting highly classified information, such as daily situation reports, battle plans,
and troop movement orders, in the clear. The analysts were amazed that the North Koreans were not bothering to encode this
incredibly valuable material. 5 It took another week before the first Top Secret Codeword traffic analysis report based on intercepts of NKPA plaintext radio
traffic was published and distributed by AFSA to its consumers in Washington and the Far East on July 11, just two weeks after
the North Korean invasion began. Three days later, on July 14, AFSA cryptanalysts at Arlington Hall broke the first encrypted
North Korean military radio message. In the days that followed, the AFSA cryptanalysts solved several more cipher systems
then being used by the North Korean combat divisions and their subordinate regiments, as well as some of the cipher systems
used by North Korean logistics units. 6
    The upshot was that in a mere thirty days, AFSA’s cryptanalysts had achieved the cryptologic equivalent of a miracle—they
had succeeded in breaking virtually all of the North Korean military’s tactical codes and ciphers, which must rank as one
of the most important code-breaking accomplishments of the twentieth century. The result was that by the end of July 1950,
AFSA was solving and translating over one third of all intercepted North Korean enciphered messages that were being intercepted.
Only a severe shortage of Korean linguists kept them from producing more. 7
    The net result was that AFSA’s spectacular code-breaking successes gave the commander of the Eighth U.S. Army in Korea, Lieutenant
General Walton Walker, what every military commander around the world secretly dreams about—near complete and real-time access
to the plans and intentions of the enemy forces he faced. James H. Polk, who was a senior intelligence officer on General
MacArthur’s G-2 staff in Tokyo at the time, recalled, “We had the North Korean codes down pat. We knew everything they were
going to do, usually before they got the orders from Pyongyang decoded themselves. You can’t ask for more than that.” A young
army field commander attached to Eighth U.S. Army headquarters at Taegu named James K. Wool-nough, who would later rise to
the rank of general, had this to say about the importance of the SIGINT available to General Walker: “They had, of course,
perfect intelligence. It all funneled in right there. They knew exactly where each platoon of North Koreans were going, and
they’d move to meet it . . . That was amazing, utterly amazing.” 8
    These code-breaking successes were to prove to be literally lifesaving over the forty-five days that followed as the vastly
outnumbered American and South Korean infantrymen of the Eighth U.S. Army tried desperately to hold on to a tiny slice of
South Korea around the port city of Pusan in a series of battles that are referred to today collectively as the Battle of
the Pusan Perimeter. Declassified documents reveal that between August 1 and September 15, 1950, SIGINT was instrumental in
helping General Walker’s Eighth Army beat back a half-dozen North Korean attacks against the Pusan Perimeter. 9 By the end of August, SIGINT revealed that the North Korean army had been reduced to a shadow of its former self. The North
Korean Thirteenth Division could only muster a thousand men for combat, while some battalions of the North Korean Fifth Division
had lost more than 80 percent of their troops, with one battalion reporting that it had only ten soldiers left on its muster
rolls. 10 SIGINT also showed that under relentless air attacks, the North Korean supply system had almost completely stopped functioning.
Ammunition shortages were so severe that it was severely affecting the combat capabilities of virtually all frontline NKPA
units deployed around