An inert U.S. Hellfire missile sent to Europe for a NATO training exercise in 2014 was mistakenly shipped to Cuba and has been there ever since. 

Though the missile does not contain any explosives, The Wall Street Journal reports U.S. officials are concerned that Cuban authorites may share the missile's sensors and targeting technology with countries like Russia, China and North Korea.

Several people familiar with the case told the Journal that the incident is the worst example of sensitive military technology falling into the hands of a nation under U.S. sanctions that they can recall.

According to the Journal report, the missile was properly shipped to Spain, where it was used in the exercise. It was then supposed to be taken on a roundabout journey back to the U.S. via Germany. Instead, the Journal reported the missile was loaded onto an Air France truck that took the cargo to Charles de Gaulle Airport in Paris, where it was put on a flight to Havana. 

The Journal reported that federal investigators were working to determine whether the shipment was the result of a major error, or the work of international criminals or spies. 

A U.S. official told the Associated Press that manufacturer Lockheed Martin was authorized to export the dummy missile for the training exercise. The official attributed the shipping error to Lockheed's freight forwarders, and said the U.S. was working with Lockheed to get the device back.

The Journal reported that the initial permission for Lockheed to send the missile to Spain came from the State Department, which declined comment

U.S. officials have been urging the Cuban government to return the missile, the Journal said, adding that officials don't suspect that Cuba will try to develop similar weapons technology on its own. The U.S. and Cuba restored diplomatic relations in July 2015 after more than 50 years of hostility.

According to the Defense Department, the Hellfire is a laser-guided, air-to-surface missile that weighs about 100 pounds. It can be deployed from an attack helicopter like the Apache or an unmanned drone like the Predator. The Hellfire training missile contains an incomplete guidance section and has no operational seeker head, warhead, fusing system or rocket motor.

The Associated Press contributed to this report.

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