I recently discovered David Shulman's anagramed "sonnet" on "Washington Crossing the Delaware," written in 1936, in Douglas Hofstadter's review of Ross Eckler's Making the Alphabet Dance, as well as Shulman's reply to that review, in which he writes: "after waiting 60 years, I find that nobody so far has equaled or surpassed it."
Hodge, Janet D.
"An Anagram Sonnet,"
Word Ways: Vol. 43
, Article 26.
Available at: https://digitalcommons.butler.edu/wordways/vol43/iss3/26