Düsenflieger is a fantastic German compound word, combining Düse (jet / nozzle) and Flieger (flyer / plane). It's a much cooler way to say "jet fighter"!
In the song, the story takes a turn when the military scrambles 99 Düsenflieger to intercept what they think are UFOs, but are really just balloons. This word perfectly captures the Cold War paranoia and military overreaction that is central to the song's powerful anti-war message.
Who knew ninety-nine toy balloons could cause the end of the world? In "99 Luftballons", German pop singer Nena sings about a harmless batch of red balloons floating toward the horizon that sparks complete military chaos. A trigger-happy general mistakes them for "UFOs aus dem All" (UFOs from outer space) and sends up a squadron of fighter jets. The pilots fancy themselves heroic space adventurers—literally singing "Hielten sich für Captain Kirk" (thought they were Captain Kirk, the famous sci-fi captain from Star Trek)—and open fire. When nearby nations see the explosions, the situation spirals out of control because "Die Nachbarn haben nichts gerafft" (the neighbors didn't get it / understood nothing; raffen is German slang for catching on or understanding).
From there, ninety-nine war ministers act like "Streichholz und Benzinkanister" (a matchstick and a gasoline canister), eager for power and ready to start a blaze over nothing. The absurd overreaction leads to a devastating conflict lasting ninety-nine years, wiping out the ministers, the jets, and everyone else until there are no winners left. By the final verse, the narrator walks through a ruined, empty world ("Ich seh' die Welt in Trümmern liegen" / I see the world lying in ruins). She finds one lone balloon left behind, thinks of you, and lets it go into the sky.