It's a quote from "Dad's Army"
Sgt. Arthur Wilson : It's a beautiful sunset, sir.
Cpt. George Mainwaring : It's a beautiful land, Wilson. They're not going to get it, you know. We shall fight them until we have just one round each, and we'll use that on ourselves!
[pause]
Cpt. George Mainwaring : By the way, how much ammunition have we got?
Sgt. Arthur Wilson : [trying not to laugh] One round each, sir!
https://www.imdb.com/title/tt0066963/characters/nm0494452