It was difficult identifying Castle Thunder records at the National Archives. There were about a dozen ledgers re the prison, but nothing I could pinpoint.

I did find a ledger containing many names, but dates were not legible.

On a page with the date heading not readable, I found:

Carr, W. F., Yankee, arrested _____, 17/18, 1863 by Captain Alex, Confined at Castle Thunder, Under Remarks: "Papers with Maj Carrington," nothing recorded in Column titled "When & Why Released," [p. 44, Record Group 109, Chapter IX, Vol. 100]

Next page starts with those captured Sept. 20, 1863, previous page ends with those captured March 14, 1863

Sorry, had I more time, I may have been more successful. The Research Assistants were helpful, but could not identify other than point me to endless indexes.