unique ID (ORDER NUMBER) for forms

unique ID (ORDER NUMBER) for forms

i have 3 forms that work as follows:

1- ORDER.... when submitted, it notifies the next department by email (which is Accounting)

2- Accounting .....when submitted, it notifies the next department by email (which is shipping )


3- Shipping..........


now , only the order form has the unique ID , however, each order has to go through 1-2-3 to be completed they should all have the same Unique ID # or Order #

please guide me !!!