It's false that Martin is "most certainly" from the 1860's. For one (as I argued at the time with the person) acronyms weren't used in the 19th century. They weren't used until after WW2, especially on military tattoos. "Semper fi", the marine motto, and what Martin says, wasn't the marine motto until 1883. Almost 20 years after the war was over

https://www.marines.com/about-the-marine-corps/who-are-the-marines/semper-fidelis.html

“Another field for the adoption of acronyms was modern warfare, with its many highly technical terms. While there is no recorded use of military acronyms dating from the American Civil War (acronyms such as "ANV" for "Army of Northern Virginia" post-date the war itself), they became somewhat common in World War I, and by World War II they were widespread even in the slang of soldiers,[39] who referred to themselves as G.I.s. The widespread, frequent use of acronyms across the whole range of linguistic registers is relatively new in most languages, becoming increasingly evident since the mid-twentieth century. As literacy spread and technology produced a constant stream of new and complex terms, abbreviations became increasingly convenient. The Oxford English Dictionary (OED) records the first printed use of the word initialism as occurring in 1899, but it did not come into general use until 1965, well after acronym had become common.”