The defence forces said it couldn't identify the nationality of the submarine, most analysts suspected it was Russian. (Representational Image)
Swedish military sighted a foreign submarine in the Stockholm archipelago during a drill last year, just six months after the biggest submarine hunt in Sweden for over two decades, daily Dagens Nyheter reported today.
A submarine periscope was observed by Swedish defense personnel during a drill in spring 2015 but was first taken for belonging to a Swedish vessel. Only later did the military realize no Swedish submarine had been in that location during the drill. The observation is classed as "probable submarine", the second highest level of certainty.
Sweden conducted the biggest submarine chase in decades in late 2014 after several sightings of a sub in the Stockholm archipelago. Although the defence forces said it couldn't identify the nationality of the submarine, most analysts suspected it was Russian.
Sweden and Finland has since extended their cooperation on defense and plan to set up a joint naval task force as the two neighbours respond to rising tensions with Russia in the Baltic region.
© Thomson Reuters 2016