A U.S. Hellfire Missile sent to Europe for a training exercise in 2014 was mistakenly sent to Cuba and has remained there ever since despite protests for its return, officials revealed Friday.

While no one knows why the Hellfire Captive Air Training Missile ultimately wound up in Cuba, the timeline suggests that the journey began when the CATM was sent to Spain by Lockheed Martin as part of a NATO training exercise, reported NPR. It was then supposed to be returned through a roundabout journey back to the U.S. via Germany. However, it inexplicably ended up in an Air France truck that took the cargo to Charles de Gaulle Airport in Paris, where it was put on a flight to Havana.

Now investigators are left to determine whether the mistake was the result of a shipping error or international espionage.

Officials do note that while the missile is inert (non-explosive), it still contains sensitive American weapons technology, including targeting and sensor information, which they fear could be shared with other world powers such as Russia, China or North Korea, according to BBC News.

"This is an issue that the administration takes very, very seriously. I think for quite obvious reasons," White House spokesman Josh Earnest said Friday when asked about the issue, according to CNN.

In the meantime, officials have been trying to get Cuba to return the missile to the U.S. for more than a year now but have been unsuccesful. The delays could be possibly be the result of the focus given to the restoration of diplomatic ties between the two countries after more than 50 years of hostility. Relations were re-established last summer, and embassies are expected to open in Washington and Havana this summer.

Hellfire Missiles are laser-guided, air-to-surface missiles that weigh about 100 pounds each. Though initially designed as anti-tank missiles to be deployed from an attack helicopter like the Apache, modern-usage has seen the missile adapted so it could be fired from unmanned aerial vehicles, or drones like the Predator, in anti-terrorism operations.