Does Miles really refer to them as “battalions”. This was a cavalry regiment — more conventionally it would be divided into “squadrons”.
Hello
squadrons was used in the cavalry in 1880
The terms battalions and squadrons were largely interchangable during this period. These were temporary, tactical formations in any case. A regiment was led by three field grade officers: A Colonel, Lieutenant Colonel, and Major. These three could each lead a battalion/squadron when the occasion required. Most regiments in this period were vastly understrength and scattered about in small outposts manned by 1-3 companies from different regiments. The regiment was only rarely mustered together, one of these rare occasions being the Little Big Horn campaign.
Custer was actually the regiment’s Lieutenant Colonel, the nominal Colonel was assigned other duties and never actually served with the regiment. This was further complicated by the use of Brevet titles, usually the rank held during the Civil War. Custer was a Brevet Major General, but really a Lieutenant Colonel in the Regular Army. Many of his officers held similar Brevet ranks that they could use by courtesy.