Maritime Force Protection Unit

A Maritime Force Protection Unit (MFPU) is a U.S. Coast Guard special unit tasked with the protection of U.S. Navy ballistic missile submarines (SSBN) while surfaced and transiting U.S. territorial waters to and from their patrol stations. Maritime Force Protection Units have approximately 150 personnel and are "single-mission" units, meaning they have no other responsibilities other than the defense of SSBNs.

Source: Wikipedia — Maritime Force Protection Unit (CC BY-SA 4.0)