Explosions, burning oil, and depth charges devastate Hårsfjärden

The Swedish fleet was exercising when Göteborg, Klas Horn, and Klas Uggla were moored together near Märsön. Stockholm, the fourth destroyer in the division, was at Mysingen and intended to moor outside Göteborg. Training aboard Göteborg involved torpedo tubes loaded with live warheads because the fleet was on wartime alert. An unexplained stern explosion aboard Göteborg was followed by another near Klas Horn, while burning oil prevented the destroyers from being towed clear. As the damaged ships settled, unsecured depth charges detonated in the water and intensified the destruction. Uggla sank after about an hour; Göteborg and Klas Horn were salvaged and returned to service in 1943. The disaster killed 33 sailors, making it Sweden's deadliest naval accident during the wartime years of readiness. Some reports attribute Uggla's irrecoverable damage to a twisted keel, while others describe different damage. Heat and underwater explosions offer a possible explanation for the keel damage, but the mechanism remains uncertain.