The Polish Maritime Museum specializes in underwater archaeological research in the Baltic Sea. The team of archaeologists and skin-divers has been working on more then 30 wreck sites until now. Wrecks, located by its own searches as well as those notified by fishermen or the Marine Office, were entered on an inventory chart and marked: W-1, W-2 etc. Most of them are wrecks of sailing ships from the 17th and 18th century. Three wrecks (W-5, W-6 and W-32) are recognized as the most important underwater sites in Poland.