How likely are officers in the army to get the job they want?

There are 2 selections you have to meet.

1. You must be chosen for active duty instead of assigned to reserve forces. Placing high on the Order of Merit List (OML) and requesting active duty is what you can control. The Army will bring in the number of active duty officers that are needed. When the military is reducing in size and there are many students going through ROTC, not everyone that wants active duty gets it.If you have a 3.2 or higher GPA and equivalent evaluations from your third year class and LDAC, you should get active if you request it (about 90% chance). If you have a 3.0 GPA you are more in the 50/50 category. From the referenced document, in FY16 there were 3762 officer wanting active duty and 3016 got it.

2. The second part is getting your first choice. Again, OML is going to be the biggest thing you can control. If you are in the top 10% of the OML, you get your choice. Armor is on the high end of competition (#5 behind - Aviation, MI, Medical Services, and Infantry). It has been running about 63-64% of cadets get their #1 choice. For Armor, the slide shows there were 119 openings and 216 cadets put it as their #1 choice.

Branch Detailing means congratulations this is your branch, now we are going to assign you to something else.

There is a program that can GUARANTEE you your branch in exchange for signing up for 3 additional years of active duty (Active Duty Service Obligation - ADSO). If you get the choice on your own, nothing changes. If you get the choice because of ADSO, you do an additional 3 years. If you don't get your choice, you don't owe the time.

Basically, the higher you rank on the order of merit, the more likely you are to get your choice.

In other words, you're at the mercy of your own efforts and the needs of the Army.

50/50. you will either get your first pick, or you won't.

IN ROTC they have a thing called the Order of Merit List

the higher you rank on the list, the better chance you have of getting your first Branch choice

Order of Merit List is based on your rating in the CDC, rating by your ROTC cadre based on the leadership labs your ROTC gpa and your Univ GPA.

Very likely

Heard its hard man, so don't beat yourself up