I have been learning German on Duolingo for most of this year. I've also been watching some TV shows in German - Arthur und die Freunde der Tafelrunde and Dark. Both of these shows have featured a character exclaiming "Attacke!" and then... well in one show, the character attacked something, and in the other, he jumped into a lake, haha. I gleefully assumed it was the imperative form of the German word that our English word (and battle cry) came from. But then I actually looked it up in linguee.de and the only entry is for a noun. Is this what they are saying? Are they just copying something English-speaking TV says? Or perhaps it's actually in first-person and they are declaring that they themselves are attacking?
How is this one-word phrase understood to a German speaker?