18th-Century Cannons Retrieved From Baltic Cannons from 1771 will take four years to clean and preserve By Newser Editors and Wire Services Posted Jun 20, 2011 9:56 AM CDT 2 comments Comments Forty cannons were found in wreckage in the Baltic Sea, three dating back to 1771. (Shutterstock) (Newser) – Polish explorers have retrieved three 18th-century cannons from shipwrecks resting on the Baltic Sea bottom. The Swedish cannons bear the minting date of 1771 and were found in the remains of a commercial and a navy ship resting more than 130 feet below, said an expert from the Gdansk Main Sea Museum. They were among more than 40 cannons and some cargo found in the wreckage. 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.