On Tuesday, a naval mine appeared floating in the waters off the coast of Bainbridge Island in Washington State, not far from Kitsap Naval Base. The contact-style mine seemed to appear out of thin air in the heavily trafficked waterway just outside of Seattle, prompting officials to instruct locals to shelter in place while Navy explosive ordnance disposal personnel dealt with the threat.

The Coast Guard established a 1,500-meter perimeter around the mine, which they referred to only as “potentially unexploded ordnance,” while Navy divers approached and inspected the mine. Eventually, they were able to secure the mine to a boat and tow it away from the Brownsville Marina it had drifted near. Once it was far enough away from shore that Navy personnel were confident that it wouldn’t pose a threat to nearby civilians or property, the EOD team detonated the mine.

You can watch that detonation below:

The exact origin of the mine remains a bit of a mystery, though one the Navy doesn’t seem to be particularly concerned about. Contact mines of a similar variety were employed heavily throughout the second World War, but admittedly, images of the mine seem to suggest that it’s in awfully good condition to be a forgotten relic of the 1940s. Navy personnel were quoted as saying that the mine had about “a decade’s worth” of organic growth on it, seeming to suggest that it had been deployed far more recently than World War II. The Navy’s behavior would seem to suggest that they’re confident in the mine’s origin, as no effort has begun to sweep the area for other potential mines. That alone would seem to suggest a high level of confidence that no others will appear.