On the afternoon of 7 July 1957, the tugboat Tyr, with a crew of four and a harbour pilot on board, departed from the quay at Slussen to assist the vessel Sunnanland. The harbour pilot was to board the vessel and guide her into Hammarbyhamnen, with Tyr’s help. Among Tyr’s crew was Bernt Thuresson. Once the pilot had transferred to Sunnanland, Tyr’s crew began the process of receiving the towing line.
As the towing line was being passed to Tyr, the tugboat manoeuvred dangerously close to Sunnanland’s bow. Thuresson managed to grab the line with a boat hook and began hauling it in, preparing to secure it to Tyr’s tow hook. Unfortunately, Tyr drifted crosswise in front of Sunnanland’s massive bow. The crew on board Tyr reacted too slowly, failing to take evasive action in time. Despite Sunnanland reversing her engines, a collision was unavoidable.
Realising the imminent danger, Thuresson rushed to the gunwale and threw himself as far from Tyr as possible. He knew that if he remained too close, he risked being pulled under or caught by the propeller as the tugboat went down. Swiftly swimming away, he was rescued shortly afterwards by the tugboat Munin.
Sunnanland continued slowly forward, pushing Tyr below the surface. Water flowed rapidly into the damaged tug, sinking stern first. All three people on board perished.
On 11 July, dives were conducted on the wreck and the body of the captain was found inside the wheelhouse. The other two crew members were not found. Dives were conducted to prepare Tyr for salvage, but since the hull was stuck in the muddy seabed, salvaging the vessel was considered too complicated.
Today Tyr lies at a depth of about 30 metres between Biskopsudden and Finnboda, partly covered by dredged material.