From Halopedia, the Halo wiki
Crewman Recruit, abbreviated to CR, is a enlisted rank in the United Nations Space Command Naval Command (NAVCOM) rank structure; including the UNSC Navy and Office of Naval Intelligence. It is subordinate to a Crewman Apprentice.
To become a Crewman Recruit, a person must enlist in the Navy. An application was required to be filled that included the question "WHY DO YOU WANT TO ENLIST?" where the applicant had to answer it in under 100 words or less.
Crewman Recruits go to boot camp and training school. In 2488, Crewman Recruits were often ordered to the Unified Combined Military Boot Camp and shipped up an elevator for vacuum and microgravity training.
In 2488, Crewman Recruits were tested with requisite physical tests, if they had any mental aberrations, a Combined Arms Skill Test, a Combined Physical Skill Test, and a Gratney-Walis Hierarchical Aptitude Score, with evaluations often from a Petty Officer First Class.
Duration start and end dates are given based on the earliest and latest information possible.