The origin of the phrase "When the balloon goes up"

[SirRay]

I have heard this phrase in stories and on TV, usually in a context implying the start of war or revolution (or just all hell breaking loose).
Anyone have a handle on it’s origin?

[Exgineer]

I can’t really verify this, but I was told it goes back to the time when hot-air balloons were used as military obsevation platforms (fitted with a telegraph, or semaphore).

When the balloon goes up, the battle is about to start.

[KneadToKnow]

Cassell’s Dictionary of Slang makes the same guess Exgineer does:

[1910s] (orig. milit.) the start of proceedings, esp. when there is a potential for controversy or argument. [? raising of an observation balloon immediately before an attack]