I'm reading John Herberich's Masters of the Field about the Fourth U.S. Cavalry (regulars). Herberich states that it was possible for an officer to have four ranks:  permanent commission in the regulars, brevet rank in the regulars, commission in volunteer service and brevet rank in the volunteer service.  So, while one could be a captain in the regulars, he could hold a brevet lt. col. as a regular, a commission as a brigadier general of volunteers and a brevet major general in the volunteers.  However, per Herberich, he only receives a captain's pay.  Can anyone confirm this?  I think that if he was a brigadier general of volunteers commanding a division because of his brevet major-general rank, he would receive at least a brigadier general's pay.  It wouldn't seem unfair that a colonel of volunteers or brigadier general of volunteers underneath him would receive more pay.

Permanent rank is often the only one the officer would get paid for.

Brevet is temporary (unless later confirmed), and the other commissions would be more like "acting" ranks, not substantive ranks.

Interesting that a commission in the volunteer service doesn't carry the pay that goes with the rank.

Different times then, and there are a lot of ranks even today that don't carry the pay of their nominal grade. See "frocking" where an officer selected for promotion is allowed to wear the rank and carry out the duties of their new rank early, but don't start getting paid or have an official promotion date until the final approvals go through.

If I had to surmise, I'd guess that a regular officer who also had a volunteer commission might only be paid at their volunteer rank when actually serving with the unit of volunteers, not while serving with other units. A West Point lieutenant appointed by a governor to be the colonel of a volunteer regiment doesn't keep that jump to colonel when they return to active duty with the regular army, and the army's still only paying them as a lieutenant, though the volunteer unit might supplement their pay while they're on duty with that unit.

Even now, it is possible for a NG officer to hold two different ranks.  The Gov. can appoint a friend as a General and he get's generals' pay while doing state work.  But, the Army might only give him federal recognition as an LTC.  If the unit is activated, he will only be a LTC and get LTC pay. Even then, the Army could "frock" him as a Col, but he would still get LTC pay. This actually happened with the KY NG a few years back.

George Custer went from a 2nd Lt on McClellan's staff to a bvt Major General in less than 2 years, after the war his rank in the regular army was LT Colonel. He died as a LT Colonel.

Go on Wikipedia and look up the dates of rank for some of the army's top commanders in WWII. It happened then too.

We just had this happen in Delaware. Our Adjutant General just retired. His official rank that he retired as is Major General. The state "promoted" him at his retirement to Lieutenant General. He retired around the same time our new governor was sworn in, and at the governor's pass in review he was "promoted" by the governor to General.

Just read a book on his last stand.  While only a Lieutenant Colonel the men still called him General.  Post-Civil War promotions were really slow in the US Army.  Another of those involved in the last stand spent 10+ years in the same battalion...