Polish explorers have retrieved three 18th-century cannons from ship wrecks resting on the Baltic Sea bottom.

Iwona Pomian, an expert at the Main Sea Museum in Gdansk, said Monday the three Swedish cannons bear the minting date of 1771 and were found in the remains of a commercial and a navy ship resting over 130 feet (40 meters) below.

She says they were among more than 40 cannons and some cargo found in the wreckage.

Pomian says it will take experts at the museum up to four years to clean the cannons and do preservation work before they can be put on display.