According to a Wall Street Journal report, a nonexplosive U.S. Hellfire Missile was accidentally sent from Europe to Cuba in 2014. Though this incident occurred more than a year ago, allowing any military technology to slip so easily into foreign hands “ranks among the worst-known incidents of its kind.”

Originally designed to bust apart tanks, hellfires are laser guided air-to-ground missiles fired from helicopters or unmanned drones at enemies on the ground. They are a staple in the American anti-terrorism arsenal, and the fact that hellfires wound up in Cuba before it reopened diplomatic relations with United States is worrisome at best, catastrophic at worst.

From the Wall Street Journal:

This particular missile didn’t contain explosives, but U.S. officials worry that Cuba could share the sensors and targeting technology inside it with nations like China, North Korea or Russia, these people said. Officials don’t suspect Cuba is likely to try to take apart the missile on its own and try to develop similar weapons technology, these people said. It is unclear whether a U.S. adversary has ever obtained such knowledge of a Hellfire.

U.S. officials said the case of the missing missile, while highly unusual, points to long-standing concerns about the security of international commercial shipping and the difficulty of keeping close tabs on important items.

“Did someone take a bribe to send it somewhere else? Was it an intelligence operation, or just a series of mistakes? That’s what we’ve been trying to figure out,” said one U.S. official.

The government is currently trying to get the missile back from Cuba and determine where it veered off course. U.S. officials “with knowledge of the situation” told the Associated Press and the Wall Street Journal that they are unsure whether this was truly an accident or an act of espionage.