You cannot enlist in the Marines specifically for MSOB assignment, so you first must become a Marine. Once you’ve accomplished that, Marines in any MOS can select to go through the process of assignment to MSOB. The selection process is outlined below according to the MARSOC website.
Assessment and Selection Program (A&S)
Once a Marine is qualified through the MARSOC Recruiters screening process, he will be assigned to the Assessment and Selection (A&S) Program.
Assessment and Selection Prepatory and Orientation Course (ASPOC)
All Sgts and below must attend the 3 week Assessment and Selection Preparatory and Orientation Course (ASPOC) held at Camp Lejeune, NC. All Officers and SNCOs are encouraged to attend ASPOC. ASPOC is a comprehensive program that teaches and conducts fitness orientated events around MARSOC Performance and Resiliency Program (PERRES). Other facets of the PERRES Program teach a Marine information on proper nutrition and techniques to maintain overall combat fitness. During ASPOC, Marines gain exposure to the units that compromise MARSOC while receiving daily mentorship by instructors who are MARSOC Critical Skills Operators (CSO’s). While attendance at ASPOC does not guarantee selection, it does give Marines an opportunity to gain knowledge and information while physically acclimating to the enviornment prior to Assessment and Selection (A&S).
Prior to attending ASPOC, Marines are encouraged to follow the 10 week A&S Preparation Guide and report progress to their recruiter. Minimum physical fitness standards to enter MARSOC will not guarantee success during the A&S process. A&S recommends that Marines should run a 250 or higher on their PFT, possess aquatic skills and confidence in the water and be able to hike up to 12 miles with a 45 pound ruck sack in 3 hours and 30 minutes or less prior to attending ASPOC. This can be accomplished by adhering to the 10 week A&S Preparation Guide.
Assessment and Selection (A&S)
A&S is mentally and physically challenging. The program is conducted 3 times a year at an undisclosed location following the 3 week Assessment and Selection Preparatory and Orientation Course.