Hawkwind
"Choose Your Masks"

They're handing out the weapons
And your armour's ready too
But the most important item
Has been left up to you
You must make a firm decision
And once it's made you'll find
That the form that you have chosen
Can entirely fill your mind

For the mask you have selected
Stands for Chaos or for Law
And you cannot take it off now
'til you're no longer in the War
And the Masks of War are grinning
And from under them you howl
Out the slogans of the part you play
For the Battle's starting now

Choose your Masks
The ranks are forming
Choose your Masks
The day is dawning
Choose your Masks
And choose the side that you'll be on
And learn the words of your new song
For the Battle will be long...
So long...