Fire At Will

[just a face]

Where does the saying fire at will come from and why is the saying "fire at will"?

[Quizmonster]

'At will' has meant 'according to your own choice' for the past 700 years or so. Attached to the instruction 'Fire!' it refers to soldiers in a battle situation who are now being ordered to shoot - not at specific targets or at a set speed - but as they think best and most effective in overcoming the enemy.

[heathfield]

To add to Quizmonster's answer...you'll have seen films where the English redcoats with their muskets are lined up in three ranks against the enemy. The officer in charge shouts out the order, 'Front rank - ready, aim, fire!', and the soldiers loose off a simultaneous volley at the enemy.
The 'Fire at will' command means 'Don't wait for the order to fire a volley, but every man fire individually whenever you want to, and continue to do so until ordered to stop'.

(Of course, there's inevitably some guy named 'Will' who comes in for some stick over the command).