My application has a main form and a subform.

Main form = deployments 

Subform = incidents - incidents responded to during each deployment. 

I have successfully linked the relationship of the two using the main form's ID. Here is my issue, if my user wants to go to the incident form to update something, he/she has no way to determine which incidents go with which deployment day (unless he/she knows the ID number, they will not). So I would like to have the date autopopulated from the deployments form to each of the incidents in the subform once submitted. I have seen something similar discussed on here before, but I can not seem to get the exact coding correct. Can someone provide an assist? 

Here is some coding information from the application IDE in case it is helpful: 

From the deployments form 

1. Date_field
   
2. (
   
3.     type = date
   
4. displayname = "Date"
   
5. alloweddays = 0,1,2,3,4,5,6
   
6. row = 1
   
7. column = 1   
   
8. width = medium
   
9. )
   
10. 
    

From the incidents form

1. 
   
2. Deployment_Date
   
3. (
   
4.     type = date
   
5. displayname = "Deployment Date"
   
6. alloweddays = 0,1,2,3,4,5,6
   
7. row = 1
   
8. column = 1   
   
9. width = medium
   
10. )
    

2. DeploymentID
3. (
4. type = picklist
5. values  = Deployment.ID
6.     bidirectional = Incidents
7.     displayformat = [ID]
8. sortorder = ascending
9. row = 1
10. column = 1   
11. width = medium
12. )

Any assistance would be greatly appreciated.