Butterfield's Lullaby

Via Wikipedia:

The bugle call was composed by the Union Army Brigadier General Daniel Butterfield, an American Civil War general who commanded the 3rd Brigade of the 1st Division in the V Army Corps of the Army of the Potomac. Butterfield wrote the tune at Harrison's Landing, Virginia, in July 1862. Taps also replaced "Tattoo", the French bugle call to signal "lights out." Butterfield's bugler, Oliver W. Norton, of Erie, Pennsylvania, was the first to sound the new call. Within months, Taps was used by both Union and Confederate forces. Villanueva (see external link "Detailed History of Taps" below) states that the tune is actually a variation of an earlier bugle call known as the Scott Tattoo which was used in the U.S. from 1835 until 1860.