grammatical number - Pluralization of acronyms ending in 'S'

What is the proper way to pluralize acronyms ending in the letter 'S'?

The particular acronym under study in this case is T.A.R.D.I.S.

The various forms I believe are correct are:

• TARDISes


• T.A.R.D.I.S.es (is it even correct to pluralize this)

Answer

Whoniverse.net and Wikipedia both use TARDISes. This follows general pluralization rules and seems to generalize to pluralizing other acronyms, e.g. radars and lasers, as well as to initialisms such as USBs, GPSes.

It seems that keeping the capital letters for acronyms, as opposed to initialisms, is somewhat uncommon, but we have WASPs, for instance.

Not everyone does, but I'm using the distinction that acronyms are pronounced as words and initialisms are instead pronounced as individual letters, as supported by Ben Zimmer in the New York Times Magazine.