Premise: USS "Kamehameha" (SSBN-642) (called "Kamfish" by her crew), a "Benjamin Franklin"-class ballistic missile submarine, was the only ship of the United States Navy to be named for Kamehameha I, the first King of Hawaii (c. 1758–1819). She is one of only two ships of the United States to be named after a monarch. She was later reclassified as an attack submarine and redesignated SSN-642.
Hypothesis: There are only two Navy ships named after monarchs.