“O Silent night shows war ace danger!”

This is a semi-famous sonnet by David Shulman titled “Washington Crossing the Delaware.” Can you see what’s notable about it?

A hard, howling, tossing water scene.
Strong tide was washing hero clean.
“How cold!” Weather stings as in anger.
O Silent night shows war ace danger!
The cold waters swashing on in rage.
Redcoats warn slow his hint engage.
When star general’s action wish’d “Go!”
He saw his ragged continentals row.
Ah, he stands—sailor crew went going.
And so this general watches rowing.
He hastens—winter again grows cold.
A wet crew gain Hessian stronghold.
George can’t lose war with ’s hands in;
He’s astern—so go alight, crew, and win!

Every line—that’s every line—is an anagram of the phrase “Washington Crossing the Delaware.” Yet Shulman still managed to produce couplets and a semblance of sense, though I must admit that metre fell overboard.