Branch Detail
The reason for Branch Detail is that some branches require a higher ratio of LT's to CPT's than other branches. i.e.. Infantry needs a lot of Platoon Leaders, while MI has relatively few LT positions. Later on MI needs those detailee's back to fill CPT positions. Those detailed attend the Donor Branch BOLC course.
Therefore, Certain branches (Donor Branches) are required to assign a specific number of their new officers to certain combat arms branches (Recipient Branches) for the individual's first tour. This is done voluntarily, in cases where someone decides they want experience in one of the Recipient Branches or because they know they have a high chance of getting detailed and want to pick which branch. Once volunteers have been assigned, the branch selects the remainder involuntarily.
For USMA 2020 the Recipient Branches were: IN, AR, FA, CM. There were several Donor Branches. Don't recall all off the top of my head, but they included: MI, SC, EN, FI, AG, and others. The numbers detailed vary: out of 58 MI slots, 28 were detailed; out of 139 EN slots,13 were detailed.
Some contend that it is beneficial for new officers to serve in a combat arms before going to their assigned branch. Others argue that missing your assigned branch BOLC and first tour experience put you behind others who didn't detail. A couple of rhetorical questions to think about:
1. If you were an Engineer Battalion Commander, which Company Commander would you prefer:
A) CPT who attended Engineer BOLC and was an Engineer Platoon Leader
B) CPT who attended Infantry BOLC and was an Infantry Platoon Leader
2. If you were an Infantry Battalion Commander, which Company Commander would you prefer:
A) CPT who attended Engineer BOLC and was an Engineer Platoon Leader
B) CPT who attended Infantry BOLC and was an Infantry Platoon Leader
3. What if other branches were in the mix: MI, FA, SC, AG, etc?