Narco-submarine doesn't sound plausible at all. Sweden has very little border control on land borders. You can drive a van from mainland Europe through Denmark

Narco-submarine doesn't sound plausible at all. Sweden has very little border control on land borders. You can drive a van from mainland Europe through Denmark and over a bridge. Or cross over from the Finnish border in the North. It doesn't make any sense to build a submarine for drug trafficking purposes when you can just drive a car or walk over the border. Typical narco-subs are not submersible at all, the bulk of the craft is below water but the conning tower is on the surface at all times. This unknown craft was under water apparently for several days. (edit: according to Wikipedia, newer narco-subs may be fully submersible, but still probably not for extended periods of time) Also, the Swedish military claims to have had "contact" and detected the craft with several sensors.