Local draft boards would keep track of who registered for the draft and assign them individual serial...

1. Local draft boards would keep track of who registered for the draft and assign them individual serial numbers.
2. The local draft board would put registered draft numbers into capsules.
3. When it came time for drafting, they'd mix all the capsules together and then select capsules at random. The serial numbers drawn represented the people who would now be drafted into military service.