The Polish navy says it is almost certain that it has located the wreck of Nazi Germany's only aircraft carrier, the Graf Zeppelin.
A Polish firm searching for oil first detected the wreck in the Baltic Sea, 55km (34 miles) offshore.
The ship's whereabouts had been a mystery since the end of World War II.
The navy investigated and said it was 99% certain that the wreck was the Graf Zeppelin. The ship, built in 1938, never saw action in the war.
The navy said it was unlikely that the 250-metre (820-foot) wreck would be recovered from the seabed, as it was at a depth of more than 80 metres (264 feet).
"Technically it's impossible to pull it out of the water," a spokesman for the Polish navy, Lieutenant Commander Bartosz Zajda told the Associated Press news agency.
After the oil company Petrobaltic discovered the wreck, the Polish navy mounted a two-day expedition to the site north of the Polish port of Wladyslawowo.
Experts used remote-controlled underwater robots and sonar photographic and video equipment to gather digital images.
The navy spokesman said there were a number of characteristics matching those of the German warship.
However, the experts were still waiting to find the name on one side of the shipwreck before declaring with absolute certainty that it was that of Graf Zeppelin.
The 33,000-ton ship, able to reach a speed of 33 knots, fitted Hitler's grandiose ambitions, but the German U-boats took priority in the battle at sea.
There are conflicting theories about how it was sunk.
Some experts believe the Germans scuttled it in Szczecin (Stettin) in April 1945, just before the Soviet Army captured the city.
Others say the Soviet navy used the ship for target practice and sank it as part of a training exercise in 1947.