"I went to bed and slept as usual, but awoke the next morning in the gray of the early dawn, and to my astonishment found that the wished-for lines were arranging themselves in my brain. I lay quite still until the last verse had completed itself in my thoughts, then hastily arose, saying to myself, I shall lose this if I don't write it down immediately. I searched for an old sheet of paper and an old stub of a pen which I had had the night before, and began to scrawl the lines almost without looking, as I learned to do by often scratching down verses in the darkened room when my little children were sleeping. Having completed this, I lay down again and fell asleep, but not before feeling that something of importance had happened to me," - Julia Ward Howe, describing how she came to write "The Battle Hym of the Republic" which was first published in the Atlantic in February 1862. She was right. Something of importance had occurred.
Sage Stossel records the full context:
Julia Ward Howe, the wife of a prominent Boston abolitionist, had visited a Union Army camp in Virginia where she heard soldiers singing a tribute to the abolitionist John Brown (who had been hanged in 1859 for leading an attempted slave insurrection at Harper's Ferry). A clergyman at the camp, aware that Howe occasionally wrote poetry, suggested that she craft new verses more appropriate to the Civil War effort, to be set to the same rousing tune.
It was the hymn that Churchill, the great Atlanticist, mandated for his funeral.