Last month, a ghostly grey business jet took off from central Sweden and headed across the Baltic on a routine spying mission.
The converted Gulfstream, caught on a tracking website, was flown by the Swedish Air Force and patrolled an area thick with Russian radar signals off the militarized coast of Kaliningrad.
Apart from a couple of unobtrusive bulges underneath, Sweden's two Gulfstream-based S102B Korpen spy planes look like any other sleek corporate jet.