It wasn't that long ago that communications were still paper tape, DD 178s and MARS radio. There was also little doubt what direction the enemy came from - the sight of smoke on the horizon from stacks or the drone of aircraft approaching your battle group. Authentication confirms the identity of the other party. Non-repudiation confirms the transaction so no one can say it didn't happen or that they participated. Confidentiality, ensured by encryption, provides privacy.
Availability means that the protection works the same way all the time.
Chips magazine covers much of the advantages and new challenges that IT-21 brings to Navy operators, but IA continues to grow in its importance. If your command is lucky, you've got enough people for dedicated IS security or, more likely, you balance the responsibility with your other network management tasks. In either case, you're up against a myriad of enemies that can come from any place at any time. Whereas, you have to know every hole and gap in your armor, they only need to work hard enough to find one. It's time to take on the fortress mentality as your info systems sail off into dangerous and uncharted waters.