A mysterious event took place in the Swedish coastal waters during the summer. The incident, which took place on 28 July 2018, included information about a mysterious submarine on the surface near the Swedish coast. The event took place in the Boson peninsula of Lidingö Island, a location close to the capital Stockholm. In the region, a black unidentified object appeared on the surface while a group practising sailing including children and youth.

According to the news reported in Dagens Nyheter newspaper which published in Sweden, no Swedish or allied submarine in the region at the time of the incident reported. According to a report published in the Guardian newspaper published in the United Kingdom, an official from the Swedish Armed Forces made a statement. The statement included information that the object was a submarine but questions about the submarine's belonging and class were left unanswered.