the meaning of "fire away"

[kjc0123]

What is the meaning of "fire away" in the following sentences?

Standard ATM machines allowed users three attempts to type a PIN before confiscating their bank card. This was obviously no ordinary cash machine.
"The number looks right," Langdon confirmed, carefully checking what they had typed and comparing it to the printout. He motioned to the ENTER key. "Fire away."
Sophie extended her index finger toward the keypad, but hesitated, an odd thought now hitting her.
"Go ahead," Langdon urged.

[Quizmonster]

'Fire away!' simply means 'Do it!' or 'Take action!' In this case, Langdon is telling Sophie to 'Press the 'enter' key!' The idea comes from soldiers firing their weapons.