On February 9, 1888, Walt Whitman penned a note to the publishers of The Riverside Literature Series No. 32 calling attention to mistakes in their recently printed version of his poem, “O Captain! My Captain!” “Somehow you have got a couple of bad perversions in ‘O Captain,'” he wrote. “I send you a corrected sheet.”

Walt Whitman Papers: Literary file; Poetry; O Captain! My Captain! Printed copy with corrections, 1888. February 9, 1888. Walt Whitman Papers (Miscellaneous Manuscript Collection). Manuscript Division

Whitman wrote “O Captain! My Captain!” in response to the assassination of Abraham Lincoln in 1865. He revised the poem in 1866 and again in 1871. Apparently, the Riverside editors published an earlier version of the poem. Whitman’s February 9 letter to the publishers details his changes for punctuation and entire lines of text.
Published to immediate acclaim in the Saturday Press, “O Captain! My Captain!” was the only poem from Whitman’s compendium, Leaves of Grass, widely reprinted and anthologized during his lifetime. Whitman rarely used rhymed, rhythmically regular verse, but here it creates a somber, yet exalted, effect.

O CAPTAIN! my captain! our fearful trip is done;
The ship has weathered every rack, the prize we sought is won;
The port is near, the bells I hear, the people all exulting,
While follow eyes the steady keel, the vessel grim and daring.
But O heart! heart! heart!
O the bleeding drops of red!
Where on the deck my captain lies,
Fallen cold and dead.

Abraham Lincoln, head-and-shoulders portrait. Douglas Volk, artist; photograph of a painting, [between 1908 and 1912]. Detroit Publishing Company. Prints & Photographs Division

By the 1880s, Whitman was asked to recite the poem so often he said, “I’m almost sorry I ever wrote [it],” though it had “certain emotional immediate reasons for being.”

Walt Whitman. John White Alexander, artist; photograph of a painting, c[between 1900 and 1920]. Detroit Publishing Company. Prints & Photographs Division

 

via https://www.loc.gov/item/today-in-history/february-09