Us army armor question- military personnel only.?

The positions on a vehicle aren't really rank related, they are more experience related. When you first arrive, you will be the driver (note to the above poster, 1st Sergeants do not have vehicles). They will let you train on the gun and you will learn to maneuver and give commands. If you do well, they will move you to the gunner's job. An M1 has 4 positions, so loader is the second job after driver. In a Bradley Fighting Vehicle (BFV) same with a Stryker, there are only 3 positions, so the 2nd job is gunner. M113s and M577s are not combat vehicles so you would only drive those if you are in the training room. Everyone cross-trains on everyone else's jobs, however, so you would learn them all and get time on them all.