David, I think you have something here regarding the 15th. Confederate Cavalry. There may be a record of this event in the O.R.'s under Shieldsboro/Shieldsborough rather than Bay St. Louis.

"Captain John H. Marshall of CO G, 15th. Confederate Cavalry with a detachment of sixteen men had a skirmish with the enemy at Shieldsboro, Miss. on 20 Oct, 1863 in which Capt. Marshall was severely wounded."

Captain Marshall was gunshot in the right shoulder with paralysis in his arm and retired 15 Nov, 1864 from the Invalid Corps, P. A. C. S.