I'm calling you out for powergaming. Think of me what you like, but that's way too much bang for your buck. $1 billion would buy only a single submarine or battleship, maybe a really cheap destroyer. An aircraft carrier costs around $5 billion each. Even if you had some already, half of the price I posted is still low for the number you have in service, and this isn't including ships that you built that are now out of service.
And dare I mention maintenance and staffing costs?
Again, the costs I posted are merely building costs.