User-created doctrines cannot be loaded in the mission editor.
The only way to make this doctrine available to platforms is to edit the SubDef doctrine or replace the SubDef doctrine.
Keep in mind, the doctrine system ALWAYS works in the following manner: the doctrine assigned in the Database to the platform is called the Platform Doctrine.
The Platform Doctrine is always running for the platform, evaluated each game cycle. This doctrine tells the platform what to do under various circumstances, with or without any other input from the sim or sensor contacts.
The other type of doctrine is the Target Doctrine. This is the doctrine that is called by the Platform Doctrine whenever a new sensor or link contact is detected by the platform AND the NewTrack variable is evaluated as True by the sim. The NewTrack variable will be evaluated as True in the Platform Doctrine exactly ONCE for each NEW sensor contact, and at this time there is the opportunity to call the target doctrine using the SETTACTIC "xxx" command.
Also, ALL platforms of the same object type in the database MUST use the same platform doctrine.
So, I'm not sure what kind of behavior your are trying to get from the submarines exactly, but getting them to do what you want and keep a functional AI takes a bit of trial and error work.
I hope this helps, feel free to get specific if you want further assistance.
Cheers,
David