[RichH]

US Coast guard has agreements with most Caribbean and most S. American countries, and many 'overseas' countries. probably except Cuba and now Venez.

The prime commission of the USCG is/was interdiction of smuggling of contraband and 'revenue' avoidance, only added lifesaving as a prime directive with the absorption and inclusion of the US Life Saving Service in ~1890s.

USCG was under the Treasury Dept. until the recent change to administration by the Dept of Homeland Security.
Can, or used to be, available to be 'transferred' to Defense Dept. (Navy) during war time.

If US flagged, a vessel can be boarded 'anywhere' by Navy or USCG.