Wiktionary
phr. (context idiomatic English) Something exciting or dangerous begins.
Usage examples of "balloon goes up".
This is what London dreams of: a rampant middle-class radical freedom movement in place, up and running, ready to blaze away for democracy as soon as the balloon goes up.
Which won't be the case if we have to do it for real, as we bloody well will when those trucks start supplying forward bases inside Solace territory as soon as the balloon goes up.
Am I to be offered, shall we say, a grandstand seat when the balloon goes up?
Which means, when the balloon goes up, everybody on this ship needs to be in spacesuits.
One of the worst parts of this job is that you have to pace yourself--when the balloon goes up, you've got to be well rested, alert, or at least able to manage a reasonable facsimile thereof.
He's got more full-time troopers than anyone else but he doesn't have a big militia he can call out when the balloon goes up.
When the balloon goes up watch out for Slade and Wheeler -- they should be doing their best to jump overboard if all goes well.