Have you looked at the Contact Management Dbase that comes with FMP? It may have more than you need and you're modifications may consist mainly of deleting fields that you don't need. You would likely want to build onto it a value list of clearance levels...
Is there a special feature(s) that you would need that aren't covered under that solution?
As you read through various things, pay some particular attention to the security of your own Dbase. That would seem particularly important for your application.
Enjoy the day!