North Korea is flexing its muscles. About 280 South Korean fishing vessels experienced problems with their GPS navigation systems. Although the jamming hasn’t caused any major problems to any vessels, the jamming comes hours after North Korea fired a short range missile into the sea out of anger at the ongoing U.S. joint military drills with South Korea.

“The disruption affected the fishing boats by making the GPS signal disappear from time to time throughout the day,” an officer from the South Korean Ministry of Oceans and Fisheries told NBC News. “But so long as the radar works, fishing boats can avoid … accidents.”

In a statement, the South Korean Ministry of National Defense said: “North Korea has been continuously disrupting GPS system since 7:30 pm [Thursday] and thereby interfering and hampering our military movements, which is threatening the safety of our people.

However, the jamming does not appear to have any affect on the military, aviation, or telecommunication systems.