In 2002, divers stumbled upon the wrecks of three Dutch warships that took 900 crew members to their watery graves during World War II's Battle of the Java Sea.

Finding them again has so far proved, well, impossible. Divers hoping to examine the wrecks ahead of the 75th anniversary of the 1942 battle found imprints of the wrecks off Indonesia using sonar, but the wrecks themselves have mysteriously vanished—one in part and two in whole, reports the Guardian.

"The wrecks of HNLMS De Ruyter and HNLMS Java have seemingly gone completely missing. A large piece is also missing of HNLMS Kortenaer," says the Dutch defense ministry, which has launched an investigation and fears the wrecks were illegally salvaged.

As more than 100 ships and submarines from World War II rest in neighboring waters, the area is known to attract salvage companies in search of steel, aluminum, and brass.

Two years ago, the US military reported an "unauthorized disturbance" at the wreck of the USS Houston in the Java Sea, while the New Straits Times reported last year that men were using explosives to rip apart wrecks for their metal.

"The desecration of a war grave is a serious offense," says the defense ministry. "The wrecks bear silent witness to the tragic events and form a backdrop to the many stories about the terrors or war and the comradeship between crew," adds the defense minister, per Dutch News.

"The Battle for Java Sea is part of our collective memory." (This wartime wreck is remarkably well-preserved.)

This article originally appeared on Newser: 3 Shipwrecks Sat on the Seabed. Then They Were Gone