Defense officials in South Korea and military analysts elsewhere are expressing concern about what they call a new type of threat from Pyongyang. The North Koreans, according to South Korea's government, are now capable of disrupting GPS receivers, which are a critical component of modern military and civilian navigation.
This week, the South Korea Communications Commission informed lawmakers that between August 23 and 25, signals emanating from near the North Korean city of Kaesong interfered with South Korean GPS military and civilian receivers on land and at sea.
Officials say the jammers were repeatedly switched on for 10-minute periods over a number of hours during the three days.
Sources in South Korea, Japan and the United States say defense officials in all three countries are concerned about Pyongyang's apparent ability to disrupt GPS navigation, and are discussing its ramifications.
Military use of GPS receivers
GPS uses up to 32 satellites operated by the U.S. Air Force. It is freely accessible to anyone with a receiver, but it has a range of critical military uses.
Retired U.S. Marine Colonel Andy Harp, a military analyst and author, notes that the military applications go beyond guiding bombs and missiles.
"It can be involved with air support, air delivery, artillery. The entire system, to a great extent, relies on GPS," says Colonel Harp.
U.S. Forces Korea spokesman Colonel Jonathan Withington declined to assess the reported North Korean jamming, saying it is a matter of intelligence and operational security.
"We also would not be able to comment on our assessment of the effects of North Korean jamming on any civilian commercial systems. While U.S. military forces do use GPS navigation technology, our forces are not reliant on the GPS to conduct ground, air or sea operations and routinely train to operate in a contested electronic environment," Willington said.
Military specialists point out that while some guided bombs might be affected by jamming, newer weapons would not be.
North Korea's culture of military creativity
Colonel Harp, who headed the Marines' Crisis Action Team that monitored developments in North Korea, is not surprised by North Korea's new ability.
"The North Koreans are great innovators," he says. "So we have to be greatly wary of what they develop and what they're capable of. The North Koreans are technologically trying to make advances across the entire front and it has to be a great concern to stay ahead of their efforts."
That sentiment is echoed by South Korea's defense minister, Kim Tae-young. He told members of the National Assembly the North Korean GPS jamming poses a "new kind of threat." Kim referred to an intelligence report saying the North Koreans can mount devices on vehicles that can jam GPS signals within a 50 to 100 kilometer radius.
Some defense analysts say while the North Korean action is unprecedented it should not have caught the South Korean military by surprise.
Professor Park Young-wook, with Kwangwoon University's Defense Industry Research Institute, says several scholars predicted the North would acquire such technology. This is the first publicly known incident attributed to North Korea, says Park. And she agrees it must be considered a serious threat if it reoccurs because GPS is an integral part of the infrastructure, not only for the military but for many other industries.
An aerospace technology consultant in Japan who did not want to be named says the August incident may have been "some sort of operational test, perhaps, to make a point."
Specifically, he says, that would be to demonstrate "a classic case of asymmetrical warfare." In other words, while the United States has invested billions of dollars in the satellite navigation system, the North Koreans can easily disrupt it with a cheap, portable transmitter on the ground.