September 17,1862 is best known as the date of the Battle of Antietam in the Civil War. Some folks call it Sharpsburg. It was the bloodiest single day of fighting in the Civil War.
Something else happened in Pittsburgh,PA that day. As in later wars,a lot of the jobs in factories/mills/plants etc. producing Civil War supplies were performed by women and children. One such place was the Allegheny Arsenal in Pittsburgh. Among other things,it produced cartridges for Union rifled and smoothbore muskets. It exploded on September 17,1862 killing 78 girls and young women. Most suffered horrible deaths from the force of the explosion or burns. About another 150 workers were injured. Found this about it in 2016 in a Civil War blog that no longer exists but is archived at the WayBack Machine:
https://web.archive.org/web/20150720184655/http://civilwarwomenblog.com/allegheny-arsenal-explosion