From my understanding when i was taught at school way back, none of my family was RAF but a couple of my teachers where.
(remember I’m dyslexic so all this American v British usage is lost on me, i just liked the story)
Back in the day the parachute was baled up into the container (parachute bag) and would be thrown by hand, so as they where getting ready to jump the order would be given to get your bale out.
I have no proof of this, its just one of the things that stuck in my head from school, before getting a clout for spelling it wrong anyway.