Contact your local recruiter and ask about becoming an infantryman. You will be wait listed for an "03XX" type contract (basic infantryman). After your first 3 months of training, you will be sent to the School of Infantry. On your 2nd month of school, you will be assigned a specific job title to replace your 03XX contract (you'll become an 0311 rifleman, 0331 machine gunner, 0341 mortarman, 0351 assaultman, or 0321 reconnaissance marine).