They don't need a CIWS, torpedos, missles and such toys when their primary mission is Search and Rescue. Secondaries are drug interdiction, alien migration interdiction and other enforcement of domestic and international laws treaties.
.50 cals come in handy when you just got done removing 600 Haitians from a 50 foot Haitian freighter and don't feel like towing it back to base. Scares the crap outta them too, makes'em think twice about trying it again. (
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