Possessives and Attributives

Q. I have a question about the possessive of a plural acronym, but where the plural is only evident in the term’s full name, not the acronym. The acronym in question is “HHS,” for (Department of) “Health and Human Services.” In the following sentence fragment, should one write HHS’s or HHS’?: “There was no better test of [HHS’s/HHS’] commitment to its mission than . . .” Thank you!

A. Treat an initialism like “HHS” as singular regardless of whether it has a plural or a singular antecedent. (Note that CMOS uses “initialism” for an abbreviation pronounced as a series of letters, like “HHS,” and “acronym” when it is pronounced as a word, like “NASA.”) To take a similar example, one would write “the United States’ allies” (following the rules for forming the possessive of a noun that’s plural in form but singular in meaning; see CMOS 7.20) but, using the initialism, “the US’s allies.” Likewise, it would be correct to write “the Department of Health and Human Services’ commitment” but “HHS’s commitment.”