Civil War Soldier and Sailor system shows him as Captain.

John B. Thompson
Regiment Name 25th Virginia Cavalry.
Side Confederate
Company A
Soldier's Rank_In Captain
Soldier's Rank_Out Captain
Film Number M382 roll 55

25th Regiment, Virginia Cavalry
25th Cavalry Regiment was organized in July, 1864, using the 27th Battalion Virginia Partisan Rangers as its nucleus. Serving in McCausland's and Imboden's Brigade, the unit fought in numerous engagements in western Virginia and the Shenandoah Valley. During April, 1865, it disbanded. Its commanders were Colonel Warren M. Hopkins, Lieutenant Colonel Henry A. Edmundson, and Major Sylvester R. McConnell.

It appears he was the only "Thompson" in Company A but there were a number of other Thompson's serving in other Companies in this unit.

Co A - Capt Sylvester P. McConnell's Co; formerly Co A, 27th Bn Va Cav; organized 8/16/1862 & served in the command when it was known as Trigg;s Bn Partisan Rangers. Captains Sylvester P. McConnell; John B. Thompson