Early in the morning in April Hanna Harge went to walk the family’s puppy when she suddenly saw something massive appear in the water outside the family’s seaside house.

“I saw this huge and odd object surface out of nowhere. Then over the next 15 minutes or so it passed by. It disappeared by the trees next to our boathouse. My first thought as that it had to be a submarine,” Harge told The Local.

She immediately ran inside to wake up her two teenage sons who hurried out to snap some photos. The pictures show what looks like a turret and the body of a submarine in the midst of the backwash of water.

The family thought it must be a Swedish navy exercise.

“My husband wanted to e-mail the military to say that residents of the area should be warned, so that no one would run into the submarine. But they answered that they had no information of any exercises in the area, “ said Harge.

The day after the family received a call and was later paid a visit by the Swedish Marine Intelligence service (Marintaktiska stabens underrättelsetjänst).

“They were here a couple of hours and questioned me and my oldest son. They reconstructed the whole event,“ said Harge.

When Harge asked the intelligence officers what they thought she might have seen they told her that it could simply be a question of floating cargo containers, according to Dagens Nyheter (DN).

But after comparing the photos with YouTube footage the family have their own theory.

“It is funny because Swedish submarines look nothing like this thing we caught on camera. But the box-like shape of the turret we saw looked very much like the Russian submarines we have since seen online,” Harge said.

They don’t think that it is likely to be a case of espionage.

“Spying by submarine just feels so ’80s’ somehow, one must assume they too have come further within that field, it just seems so dated. Instead we believe that it has to do with some sort of smuggling,” Harge said.

The family decided to take the picture to the Swedish media on the advice of a journalist friend of the family.

“But it felt right to wait for a while, as the intelligence officers that visited us were certainly treating this as a serious matter,“ she told The Local.

The Swedish military are reluctant to comment on what they think that the sighting was.

“We are examining the photographic evidence to see what it could be. But the investigation is by no means finished,“ said Marie Tisäter from the Swedish military information department to DN.

According to the Swedish military they will have finished the investigation within the next two months.