In his autobiography, Andrew notes:

"I became tired of infantry service, and as I had a dear friend in the Richmond Howitzers, I obtained from General George Bankhead MacGruder a special transfer to the Howitzers, of Richmond city, then stationed at Yorktown, Va.

"I was not at the Battle of Bethel [6/10/61], the first field fight of the war, as I did not join tlie Howitzers until after that engagement—could not get my transfer any sooner."

It's not unusual for clerks to have termed "transferred" as "dischargde" or vice versa.