(I’m not sure if this is a valid question here†, as the phrase is arguably not common enough to be classed as a fixed expression.)
Is there an ascertainable origin of Peace Through Superior Firepower?
It’s most probably a derivation of “peace through strength”; there are citations of its first appearance in a 1988 episode of Star Trek: The Next Generation, but Wikipedia only knows a music DVD by this title, Urban Dictionary cites no quotes, and while image seaches yield many gatling guns and patches with this slogan, Quora references a removed Wikipedia entry (lack of sources) and a 2001 novel by John Ringo.
Even though this is perhaps impossible to answer definitively, it’d be interesting to know if say Star Trek writers first came up with this motto.
† … or if it’s rather suitable at scifi, asking: “Was Star Trek the first to come up with ~?”
‡ There are hundreds of thousands of web results, but incomparable ngram graphs.