American soldiers guarding nuclear weapons in Europe have used online flashcard apps to study for their jobs, in the process “inadvertently revealing a multitude of sensitive security protocols about U.S. nuclear weapons and the bases at which they are stored,” according to open-source intelligence collective Bellingcat. Some publicly-visible flashcards spotted by Bellingcat researchers specified the exact number of surveillance cameras and their locations on certain bases, security features and unique identifiers found on restricted area badges, and secret duress words used by base personnel. They’ve also exposed buildings where keys to aircraft shelters are kept, locations of backup generators, and details of release codes that open the vaults in which nuclear weapons are stored. Some of the flashcards had been viewable online since 2013, according to Bellingcat, which said the information covered the time period up to at least April 2021.

“It is not known whether secret phrases, protocols or other security practices have been altered since then,” researcher Foeke Postma wrote. “However, all flashcards described within this article appear to have been taken down from the learning platforms on which they appeared after Bellingcat reached out to NATO and the U.S. Military for comment prior to publication.”