North Korean jamming of GPS shows system’s weakness

U.S. and South Korean military commanders will be on the lookout for North Korean efforts to jam GPS signals as they take part in exercises on the divided peninsula this week and next.

North Korea repeatedly has jammed GPS signals in South Korea, which has “very serious implications” because U.S. and South Korean military system rely on the navigation system, said Bruce Bennett, a North Korea scholar for the California think tank Rand Corp.

The jamming also underscores the vulnerability of a satellite-based tool on which civilian systems from car navigation to air traffic control rely upon.

North Koreans have used Russian-made, truck-mounted jamming gear near the border to disrupt low-power GPS signals in large swaths of South Korea. By broadcasting powerful radio signals on the same frequencies as the satellites, the jammers drown out the GPS signals.

Mr. Bennett said the jamming has occurred three times in the past two years and has coincided with joint U.S.-South Korean military exercises.

The timing strongly suggests the jamming was “an experiment … a test … to let [the North Koreans] see what effect it would have and maybe disrupt the exercises,” he said.

Defense officials declined to comment on the jamming, or discuss what measures U.S. forces are taking to guard against further incidents during this week’s exercises, which end Aug. 31 and involve more than 80,000 troops from the United States and South Korea, plus observers from seven other countries.

“The U.S. Department of Defense takes all jamming seriously,” said Air ForceLt. Col. Damien Pickart, a spokesman for U.S. Pacific Command.

For North Korea, the jamming is an attempt to turn the tables on the more technologically advanced U.S. and South Korean forces.

“Neutralizing those [technological] advantages could have big psychological benefits in peacetime and major military benefits in war,” Mr. Bennett said.

He added that the jamming equipment is easy to locate because of the powerful signals it broadcasts. “If you use this kind of weapon, you must assume that sooner or later, the other guy is going to destroy them,” he said.

Determining how North Korea might use the jamming as a weapon is difficult because its military does not produce publications, unlike China’s, which publishes academic journals and policy documents, Mr. Bennett said.

“The way we try to understand North Korean [military] doctrine is watching how they train and exercise,” he said.

In September, there were reports that North Koreans were developing their own, more-powerful jamming technology. Mr. Bennett said it appears that this new equipment was being tested in the most recent jamming incidents in March and April.

The incident in April caused the most significant disruption, even though the jammers were switched on only intermittently. The South Korean capital, Seoul, is only a few miles from the border, and its airport, Incheon International, was badly affected by the jamming. Aircraft had to rely on alternative navigation aids, and even cars in the city’s northern suburbs found their GPS equipment affected.

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