Estonia's military chief, Martin Harem, has raised concerns about Russia's secret electronic warfare system, Tobol, interfering with GPS systems of airliners and ships from Finland to the Baltic states and Poland. The GPS malfunctions pose a threat to both military and civilian navigation systems. While it is unclear whether Russia is achieving a specific aim or testing their equipment, the interference is especially problematic in times of conflict. The Tobol device is suspected to be located at Russia's military base in Kaliningrad.