An F-35 fighter is seen at Volkel Air Base in the Netherlands. (Photo by Reuters)

American troops tasked with guarding US nuclear arms in Europe have inadvertently exposed the exact location of the strategic weapons and their top-secret security protocols, according to a report.

An investigation by Bellingcat alleges that soldiers attempting to learn intricate security protocols about the US nuclear arsenal in Europe used popular education websites to create digital flashcards and uploaded related sensitive information on the internet.

The soldiers used popular education apps like Chegg Prep, Quizlet and Cram as part of revision exercises to help them memorize information such as which shelters had hot vaults with live nuclear bombs and their identification badge details.

By simply searching online for terms publicly known to be associated with nuclear weapons, Bellingcat was able to discover cards used by military personnel serving at all six European military bases reported to store nuclear devices, the investigative website reported.

The US Air Force has launched an investigation into the suitability of information shared via study flashcards.

The flashcards, which were publicly available to view but have now disappeared, also contain information about the positions of cameras at the bases, the frequency of patrols around the vaults, secret duress words that signal when a guard is being threatened, and the unique identifiers that a restricted area badge needs to have.

The cards had been uploaded as long ago as 2013 to the internet and were publicly available as recently as April this year.

The presence of US nuclear weapons in Europe, first deployed during the Cold War to act as a deterrent against the Soviet Union, has long been the subject of debate and controversy in the host countries.

While information on the strategic weapons and their whereabouts is scarce, various leaked documents have indicated that the United States is using at least six sites across Europe to store the arms.

In 2019, a document, written for the Defense and Security Committee of the NATO Parliamentary Assembly, made a passing reference to the roughly 150 US nuclear weapons being stored across the continent.

These bombs are stored at six US and European bases - Kleine Brogel in Belgium, Büchel in Germany, Aviano and Ghedi-Torre in Italy, Volkel in The Netherlands, and Incirlik in Turkey, one line read, according to the Belgian newspaper De Morgen.