There was no such thing as an "Honorable Discharge" in civil war days for Confederate soldiers. He was captured by Federal troops and spent over a year in a prisoner of war camp. That alone provides proof of his "honorable" service up through the final month of the war. Again, there were no muster rolls of his company which survived to be compiled, without these, we have no way of knowing when and where he enlisted. The widow's pension application papers very well might provide the dates and place of his enlistment, either from her memory, or those of his fellow soldiers who may have validated his service through an affidavit in her papers.

There is a glitch however, the Tennessee Board of Pension Commissioners prohibited granting of pensions to any soldier who signed an oath of allegiance to the US prior to Lee's surrender at Appomottox April 9,1865. I understand the Daughters of the Confederacy (UDC) apply this same standard for membership.
This was not the case for other states. Hence, this should not stand in the way of your present day efforts. I don't believe anyone today would consider his service to be anything other than honorable

John signed his oath of allegiance in March which would have disqualified him from a Tennessee pension. You would have to see if his widow was granted a pension. If so, you should be home free from the old Tennessee requirements.

The information I provided earlier is taken from his Compiled Service Record file. These papers should also be ordered along with the widow's application papers through the service noted in the Red enclosed box above.

I would suggest you obtain assistance from a member of the Sons of Confederate Veterans near you.

One may argue about the closeness of his oath re Lee's surrender. However, the Pension commissioners were hide bound. I have evidence of one Lt. grievously wounded on three occasions and hospitalized for long periods each time. The last at the Battle of Franklin, Tenn., Nov. 30, 1864. The Confederates had no nearby hospitals, however, he was able to make it home near Nashville for recuperation. Because his home was in the zone of Federal occupation, he felt it necessary to turn himself in to the Yankees to prevent retaliation against his family. He was, none-the-less, denied a pension UGH!.

John R. W. Lannon enlisted as a Private in Company B, 11th Tennessee Cavalry, captured at Cathey Creek, Tennessee December 22, 1863, forwarded to Louisville, Kentucky January 12, 1864, sent to Rock Island Barracks prison camp, Illinois January 17, released on taking the Oath of Allegiance March 24, 1865, age 33, resident of Lebanon, Tennessee, dark complexion, light hair, blue eyes, 6' tall [there are no company muster rolls for Company B, thus, we have no information on his enlistment date or attendance information thereafter]

M268: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Tennessee