Researchers have discovered the wreckage of a German submarine that sank during World War I in the North Sea, with bodies of 23 crew members, BBC reported on Tuesday. The German embassy has been informed.

The UB-II type submarine is said to be in a good condition, and was found at a depth of 30 metres off the Belgian coast. “It’s quite amazing that we found something like this,” Western Flanders Governor Carl Decaluwé told AP. “The impact damage was at the front, but the submarine remains closed and there are 23 people still on board.”

The vessel is believed to have been sunk by a mine. Decaluwé told reporters on Tuesday that the location of the wreck was being kept under wraps so that people do not go near it.

Of the 11th such wreck found in the Belgian waters, this vessel is said to be the best preserved, the BBC reported. U-boats were part of Germany’s naval campaign in the North Sea during World War 1 to target the allied powers. The UB-II type submarines were built in 1915 and 1916.