Actually it's not far off. The Coast Guard regularly escorts Washington State ferry boats across Puget Sound, especially from Seattle to Bainbridge. They use rubber boats (well, BIG rubber boats) with what looks like a .50 calibre mounted on the bow. (Too far away to identify exactly.) Last time I was on a boat we had two, fore and aft, ride the whole way. The ferries have been identified as a 'terrorist target' so we get the random export. they also take pictures of our license plates, use bomb-sniffing dogs on the docks, etc.
Did you say you were targeting "ferries" with a .50 cal?lol