knew about the estimated strength and position of
the Chinese forces. While American units had obtained some intelligence from two captured Chinese soldiers, everything else
that Eighth Army G-2 believed to be true about Chinese PLA troop dispositions was pure speculation. 41
But while AFSA was producing no intelligence about the Chinese forces, it continued to generate vast amounts of data about
the North Korean military forces because of its continued ability to read all major North Korean ciphers. According to a declassified
NSA history, as of December 1950 AFSA was solving and translating 90 percent of the encrypted North Korean messages it was
intercepting. 42 For example, SIGINT derived from these communications was instrumental in allowing the U.S. Navy to successfully evacuate
by December 24 the entire U.S. Tenth Corps plus tens of thousands of refugees from the North Korean port of Hungnam. SIGINT
also confirmed that the Chinese and North Koreans did not intend to disrupt the evacuation by air attack. 43
The Chinese January 1951 Offensive in Korea
On New Year’s Eve, December 31, 1950, seven Chinese armies launched a major offensive across the 38th parallel, which shattered
the Eighth U.S. Army’s defensive positions along the Imjin River. Seoul fell for a second time on January 4, 1951, the last
U.S. forces having fled the city the night before. 44
As American forces struggled to keep a foothold in Korea, there was little SIGINT to offer by way of intercepts of Chinese
military radio transmissions because of a lack of Chinese linguists, and also because almost all available radio intercept
resources were focused on the more productive North Korean military target. As a result, the SIGINT organizations were producing
virtually nothing in the way of usable tactical intelligence on the Chinese military at a time when U.S. field commanders
in Korea were desperate for any tidbit of information. 45
Despite these inherent weaknesses, SIGINT performed brilliantly during the month of January, helping Lieutenant General Ridgway’s
Eighth Army decimate the newly rebuilt North Korean Second and Fifth Corps as they strove to break through the American–South
Korean defensive lines in the Korean central highlands. When the South Korean Second Corps collapsed, it was SIGINT that revealed
the North Korean attack plans, with a decrypted January 2 message from the North Korean general staff in Pyongyang ordering
the commander of the North Korean Fifth Corps to push through the breach and “pursue the enemy, not giving them time to rest.” 46 By January 15, Eighth Army G-2 was convinced from an accumulation of information derived from SIGINT that the Chinese and
North Koreans were readying themselves for yet another major offensive. But SIGINT revealed that the enemy forces had taken
murderously heavy losses in the fighting up to that point, and that certain key units were barely combat ready. Another critically
important piece of intelligence provided by SIGINT was a January 23 decrypted message revealing that the entire Chinese Ninth
Army Group was reforming near the North Korean port of Wonsan and would “take a rest until the end of February.” Ridgway now
knew that three Chinese armies would not be taking part in the upcoming Chinese–North Korean offensive. 47
Acting on this intelligence, on January 24, Ridgway launched a counterattack called Operation Thunderbolt, which by January
31 had forced the Chinese forces back toward Seoul. By the end of January, SIGINT revealed that the Chinese and North Korean
forces were exhausted, short of ammunition and supplies, and decimated by battlefield casualties and infectious diseases. 48
The Ides of March: The Russians Are Here!
In late March 1951, an event took place that literally overnight changed the way the entire U.S. intelligence community thought
about the war in Korea. According to declassified documents, on March 30 the U.S. Air Force radio intercept unit in
the Chinese forces. While American units had obtained some intelligence from two captured Chinese soldiers, everything else
that Eighth Army G-2 believed to be true about Chinese PLA troop dispositions was pure speculation. 41
But while AFSA was producing no intelligence about the Chinese forces, it continued to generate vast amounts of data about
the North Korean military forces because of its continued ability to read all major North Korean ciphers. According to a declassified
NSA history, as of December 1950 AFSA was solving and translating 90 percent of the encrypted North Korean messages it was
intercepting. 42 For example, SIGINT derived from these communications was instrumental in allowing the U.S. Navy to successfully evacuate
by December 24 the entire U.S. Tenth Corps plus tens of thousands of refugees from the North Korean port of Hungnam. SIGINT
also confirmed that the Chinese and North Koreans did not intend to disrupt the evacuation by air attack. 43
The Chinese January 1951 Offensive in Korea
On New Year’s Eve, December 31, 1950, seven Chinese armies launched a major offensive across the 38th parallel, which shattered
the Eighth U.S. Army’s defensive positions along the Imjin River. Seoul fell for a second time on January 4, 1951, the last
U.S. forces having fled the city the night before. 44
As American forces struggled to keep a foothold in Korea, there was little SIGINT to offer by way of intercepts of Chinese
military radio transmissions because of a lack of Chinese linguists, and also because almost all available radio intercept
resources were focused on the more productive North Korean military target. As a result, the SIGINT organizations were producing
virtually nothing in the way of usable tactical intelligence on the Chinese military at a time when U.S. field commanders
in Korea were desperate for any tidbit of information. 45
Despite these inherent weaknesses, SIGINT performed brilliantly during the month of January, helping Lieutenant General Ridgway’s
Eighth Army decimate the newly rebuilt North Korean Second and Fifth Corps as they strove to break through the American–South
Korean defensive lines in the Korean central highlands. When the South Korean Second Corps collapsed, it was SIGINT that revealed
the North Korean attack plans, with a decrypted January 2 message from the North Korean general staff in Pyongyang ordering
the commander of the North Korean Fifth Corps to push through the breach and “pursue the enemy, not giving them time to rest.” 46 By January 15, Eighth Army G-2 was convinced from an accumulation of information derived from SIGINT that the Chinese and
North Koreans were readying themselves for yet another major offensive. But SIGINT revealed that the enemy forces had taken
murderously heavy losses in the fighting up to that point, and that certain key units were barely combat ready. Another critically
important piece of intelligence provided by SIGINT was a January 23 decrypted message revealing that the entire Chinese Ninth
Army Group was reforming near the North Korean port of Wonsan and would “take a rest until the end of February.” Ridgway now
knew that three Chinese armies would not be taking part in the upcoming Chinese–North Korean offensive. 47
Acting on this intelligence, on January 24, Ridgway launched a counterattack called Operation Thunderbolt, which by January
31 had forced the Chinese forces back toward Seoul. By the end of January, SIGINT revealed that the Chinese and North Korean
forces were exhausted, short of ammunition and supplies, and decimated by battlefield casualties and infectious diseases. 48
The Ides of March: The Russians Are Here!
In late March 1951, an event took place that literally overnight changed the way the entire U.S. intelligence community thought
about the war in Korea. According to declassified documents, on March 30 the U.S. Air Force radio intercept unit in
Similar Books
