A 16th-Century Shipwreck Was Just Found Off Sweden’s Coast Still Intact Enough to Reveal Its Tree Rings

The sonar ping was a routine occurrence, but it revealed something extraordinary during a training exercise in the Baltic Sea in late 2025. The crew of a Swedish submarine rescue ship, announced by the County Administrative Board of Kalmar County, was training when the signal returned something no one expected: a wooden ship lying on the seafloor, intact after more than four centuries.

The discovery, made possible by the timber analysis, is a warship from the late 1500s. It now ranks among the oldest vessel finds in the Kalmar Strait, the narrow channel between Sweden’s southeastern mainland and the island of Öland. The HMS Belos, assigned to the First Submarine Flotilla, was running sonar, remotely operated vehicles, and dive drills when the wreck appeared on screens.

A Training Mission Turns Into a Historic Discovery

“For the navy and HMS Belos, these types of operations and exercises are valuable because multiple parts of the ship’s crew get to train when different types of resources are used, such as sonars, remotely operated vehicles, and divers,” said Sofia Löveborn, communications chief for the First Submarine Flotilla. The crew pivoted from exercise to investigation without altering their core methods.

The discovery has sent shockwaves in the archaeological community, as it is believed to be older than the Vasa, the Swedish warship that sank in 1628 and later became one of the country’s most visited museum pieces. The County Administrative Board of Kalmar County has issued regulations that ban anchoring, diving, and fishing at the location, and the Swedish Coast Guard runs patrols while documentation continues.

The Baltic Sea: A Preserver of History

The Baltic Sea’s unique chemistry has allowed the ship to remain intact for centuries. Its brackish water, cold depths, and lack of oxygen make it an ideal environment for preserving shipwrecks. The ship uncovered by HMS Belos now joins a growing list of discoveries in the Baltic Sea, including a Swedish naval wreck near Stockholm and a shipwreck containing champagne and wine stashes.

Unraveling the Secrets of the Past

Dendrochronology, the study of tree rings, has revealed that the ship was constructed in the closing decades of the 1500s. No ship name has surfaced yet, but researchers expect further study to clarify shipbuilding methods, trade routes, or naval deployments from a time when Sweden was tightening its hold on the Baltic.

“The data gathered so far from the wreck shows that it contains unique historical and archaeological information,” said Lars Einarsson, a maritime archaeologist at the Kalmar County Museum. The County Administrative Board of Kalmar County has commissioned a protection and management plan from the museum, drawn up with the Armed Forces and the Belos crew.

No one has discussed raising the ship, and most Baltic wrecks remain on the seabed, preserved in place as underwater archaeological sites. The discovery has thickened the maritime archaeology record of the Kalmar Strait, and researchers expect further study to clarify the history of the region.

The Swedish Coast Guard runs patrols while documentation continues, and the site is now listed as an ancient monument in the national cultural heritage register. The County Administrative Board of Kalmar County has issued regulations that ban anchoring, diving, and fishing at the location.