M26 mine blows up. Source: Estonian Defence Forces

In the summer of 1941, the former Soviet Union suffered the greatest naval defeat in its history as it tried to evacuate the capital of Tallinn, Estonia. More than 80 ships were sunk and at least 12,000 people died.

Nearly 80 years later, some of those wrecks were possibly found by the participants of Open Spirit 2018. Hosted each year by one of the three Baltic states, the exercise focuses on pooling international expertise in mine warfare to deal with wartime ordnance that still threatens safe seafaring in the region. Over the past two decades, some 1,200 explosive devices have been found off the coast of Estonia alone.

The U.K.’s Royal Navy contingent from Fleet Diving Unit 3, one of three elite teams who protect Royal Navy shipping from mine threats worldwide, focused their efforts around the small island of Muhu at the entrance to the Gulf of Riga, working with more than 60 frogmen from Estonia, the U.S., Canada, Poland and Latvia.

The Royal Navy divers found nine mines, which were either blown up on the spot or towed to a safe area offshore and away from environmental protection areas. The mines were disposed of by counter-mining using a small quantity of plastic explosives in a controlled explosion. The Soviet M26 mine safely disposed of in the video is one of nearly 17,000 laid by the Red Navy in 1941 to stem the German advance.