Footage and eyewitness accounts of an unidentified submarine surfacing near a sailing camp outside of Stockholm, Sweden, over the summer were released to the public earlier this week. The footage clearly shows a fairly small (by American nuclear submarine standards) submarine fitting military characteristics surface, where it remained for about 20 minutes before submerging once again.

Rumors that the submarine may have been Russian have already made their way around the internet, thanks to decades of Russian submarine activity in the region. However, it seems likely that the unidentified submarine sails under a Swedish flag. The Swedish government has not openly claimed ownership of the wayward sub that startled the group of children and teenage sailing instructors, but they have stated clearly that the Swedish military does not consider it a sighting of a “foreign sub.”

“We can confirm that we have received information about an alleged observation in this area at that time,” Swedish armed forces spokesperson Jesper Tengroth told local media outlets this week.  “We will not comment on any further actions that we have taken or will take. We neither comment on results nor our view of alleged sightings.”

However, another unnamed spokesperson (potentially Tengroth, as well), told a different Swedish newspaper called Dagens Nyheter that the military investigation into the incident did not reveal the presence of a foreign submarine.

“The military does not share Dagens Nyheter’s view that this was a foreign submarine,” the spokesperson said before refusing to elaborate any further.

It seems possible that the submarine may have been suffering some sort of mechanical complication while conducting routine coastal operations, or that the submarine’s mission was not one the Swedish government would like to publicize  — either would explain their reluctance to lay claim on the submarine or its sudden appearance near a group of local kids. If nothing else, Swedish submarines — widely considered to be among the most capable diesel powered submersible platforms on the planet — could be regularly patrolling the nation’s coastal waters as a part of a defensive stature prompted, in part, by confirmed reports of a foreign submarine (assumed to be Russian) successfully infiltrating and then escaping Swedish waters in 2014.

“The government considers this to be extraordinary serious,” Swedish Prime Minister Stefan Lofven said at the time. “Those who consider to enter Swedish territory shall understand what huge risks it will mean in the future.”

Sweden is no stranger to fielding capable submarines themselves. In a series of naval war games held in 2005 that have since become legendary within the defense community, a single Swedish diesel-powered submarine managed to infiltrate the USS Ronald Reagan strike group and successfully “sink” the Nimitz class aircraft carrier on multiple occasions.

Of course, these war games didn’t involve any live ordnance, but the stealthy Swedish submarine was characterized as “running rings” around the massive carrier and its accompanying support vessels. When it was all over, the United States Navy paid Sweden to lease the submarine that so readily defeated them (the HSMS Gotland) in order to find more effective ways to counter submarines with similar Air Independent Propulsion (AIP) systems. China and Russia have both since begun fielding similar AIP diesel-powered submarines.

The Swedish diesel-powered attack submarine HMS Gotland transits through San Diego Harbor during the ÒSea and Air ParadeÓ held as part of Fleet Week San Diego 2005. (U.S. Navy)

It seems most likely that the submarine shown in the above video does belong to the Swedish Navy, especially considering the measured response when compared to previous submarine sightings that were confirmed to be foreign. In that case, the only mystery seems to be: why won’t the Swedish government acknowledge it?

And that’s a question that may never be answered.