I could not locate a record for William Brainerd Spencer in any Louisiana unit.

………

A. N. Spencer, 3rd Lieutenant, Capt. Alex. Mason’s Company (Catahoula Greys), 11th Regiment Louisiana Volunteers,* enlisted August 2, 1861 at New Orleans for the war, promoted 1st Lieutenant, no date, captured near Natchez March 28/April 1, 1864, sent to Johnson’s Island May 12, 1864, received at Depot Prisoner of War, near Sandusky, Ohio May 18, transferred to Point Lookout, Md. for exchange February 16, 1865, no further information

Note: The unit information for Company G, 11th Infantry, show that he was dropped from the rolls August, 1862. Card No. 12 of his file indicate he was discharged August 25, 1862. This date agrees with the transfer of Company G to the 13th Infantry. Apparently these men kept their identification with the 11th thereafter, even though assigned to the 13th. His name does not appear on the records of the 13th.

* This company subsequently became Company G, 11th Regiment Louisiana Infantry

The 11th Regiment Louisiana Infantry was disbanded August 19, 1862. Companies C, D, E, F and G were assigned to the 13th Regiment Louisiana Infantry.

M320: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Louisiana

…….

See also: http://www.acadiansingray.com/11th%20Regt.%20Inf.htm

…….

On November 30, 1862, General Braxton Bragg ordered the consolidation of the regiment [13th Louisiana] into five companies. These companies joined five companies of the 20th Louisiana Regiment to form the 13th and 20th Louisiana Consolidated Regiment. Despite the merger, promotions of officers continued as though the regiments were still separate.
http://www.acadiansingray.com/13th%20Regt.%20Inf.htm#13th%20Regiment%20Volunteer%20Infantry