I’m trying to locate information about my gg grandfather's service in the CSA. Alabama Archives says he was in the Cavalry, 1st & 15th Alabama Regiments, Company H.

I’m having difficulty understanding what and where the 1st Alabama Cavalry served and how Lang Mills could have also served in the 15th. Some readings say the 15th was made up of the 1st Alabama Regiment and the Florida Cavalry. Can you help me understand it? I’m particularly interested in where my gg grandfather served and possible battles he may have seen.

My gg grandmother's pension application says he was in the "First Alabama Volunteer Cavalry" for 3 years, enlisting in the spring of 1862. A letter from the War Department, dated 1933, says "Lang Mills, private Co., H, 15th Regt., Confederate Cav., also known as 1st. Regt. Ala., and Fla. Cav., enlisted August 2nd, 1863, at W. Pascagoula and on muster roll dated June 30, 1864 (last on file) is shown Present. Prisoner of war records show him surrendered at Citronelle, May 4th, 1865, and paroled at Mobile June 17th, 1865."

Any direction would be greatly appreciated.