The marker for Battery E, 1st U.S. Artillery is on the north side of the Boonsboro Pike, east of Rodman Avenue. (Boonsboro Pike tour map)

From the marker:

U.S.A.

Battery E, 1st U.S. Artillery 

Lieut. Alanson M. Randol, U.S.A., Commanding.

(September 17, 1862.)

Early in the afternoon of the 17th, Battery E, 1st U.S. Artillery, crossed the Antietam by the Middle Bridge and relieved Robertson’s Battery (B and L, 2d U.S. Artillery) which was in position on a knoll about 80 yards south of this point. It opened a fire of spherical case on the flank of one of the Confederate Batteries on Cemetery Hill compelling it, apparently, to retire beyond the range of its guns. As the position was an unfavorable one for the use of Artillery and subjected to an annoying fire of the Confederate skirmishers, the Battery was withdrawn and recrossed the Antietam.

No. 96.

See more on the history of the 1st United States Artillery, Battery E in the Civil War