I was looking up Robert Simpson of the 54th Ohio who survived the General Lyon Disaster and was listed as being in Co. S of the 54th Ohio. I know of no other Company "S"'s in the service so imagine this must have been a mistake.
That he would have been on the General Lyon is no surprise as his regiment was part of General Sherman's March Through the Carolinas and had taken part in the Battle of Bentonville March 20, 21, 1865.
The regiment organized at Camp Dennison, by Cincinnati, in 1861 and saw its share of hard fighting, including Vicksburg, the Atlanta Campaign, March to the Sea, then Carolinas Campaign.
It was at the Battle of Bentonville March 20-21, Occupation of Goldsboro, N.C. March 24th, Advance to raleigh April 10-14 and Johnston's surrender at Bennett House April 26th.
I was unable to learn how Private Simpson came to be on board the General Lyon, but it might have been after Bentonville. Perhaps he was wounded?
--Old Secesh