WAS is short for Weapon Action Switch - the control used to ‘Action’ (ready for firing) a weapon.
In-game these are the 1, 2 and 3 keys for the M230, rockets and hellfires respectively.
To WAS, or action, a weapon simply press its WAS button. To De-WAS, or De-action a weapon that is actioned, just press its WAS button again.
Note: You can not WAS any weapons or ARM the aircraft while on the ground, to override this you must push the GND ORIDE button.
Warning: Even if a weapon is actioned, you cannot fire it until the aircraft is armed.
Important: To arm/safe the aircraft, you click the arm/safe button on the armament panel.