From the 1950s through the 1970s, Esperanto was used by the US Army for war games, as the language of the "Maneuver Enemy", also known as the "Aggressor". The goal was an added touch of realism, with the enemy speaking a "foreign" language. Spanish was the original candidate for Aggressor's national language, but it was soon superseded by Esperanto.
Ĉu vi parolas la Agresantan?
Field manuals of particular interest...