I finally managed to winnow through all of the resignations and compare them by regiment. Some of the results were interesting.
Of the 171 officers assigned to the three mounted arms at the beginning of 1861 (1 brigadier general and 34 officers assigned to each regiment), a total of 74 resigned, or 43%. Three of the five regiments lost 50% or more of their officers, and these were the last two regiments to reach the major theaters of fighting.
Despite claims in 1855 (and later) that they were formed to accommodate southern officers, the two cavalry regiments were not the hardest hit by resignations. The most resignations came from the 2nd Dragoons/2nd Cavalry with 19. Interestingly enough, the least number of resignations came from the other dragoon regiment with 9. As I derived these numbers only from 1861, I have to wonder how many 1st Dragoon/1st Cavalry officers wanted a free ride home from the west coast before tendering their resignations. The regiment didn’t completely close on Washington DC until the end of January 1862.
The results by regiment:
1st Dragoons/1st Cavalry: 9 of 34
2nd Dragoons/2nd Cavalry: 19 of 34
Regiment of Mounted Rifles/3rd Cavalry: 10 of 34
1st Cavalry/4th Cavalry: 17 of 34
2nd Cavalry/5th Cavalry: 18 of 34