What is an MOS job in the military and how does it work?

I'm trying to figure out what an MOS job is in the military and how it determines what role someone would have. Can someone explain how MOS jobs are assigned and what factors influence these assignments?

An MOS job, or Military Occupational Specialty, refers to the specific jobs and roles available within the branches of the U.S. military, such as the Army, Marine Corps, Air Force, Navy, and Coast Guard. Each MOS job is associated with a code that denotes a specific role or task, and it could range from combat roles to supportive roles, like mechanics, intelligence, medical services, logistics, etc.

The process of assigning MOS jobs is multi-faceted and involves several key aspects. There are a few main factors that can influence the assignment of an MOS, including:

1. ASVAB Scores: A critical factor in the MOS determination process is the score a recruit receives on the Armed Services Vocational Aptitude Battery (ASVAB). This test measures a recruit's aptitude in various areas such as math, science, reading comprehension, and mechanical comprehension, and the results are used to match individuals with suitable jobs.

2. Physical Fitness: Many roles, particularly those in combat or physically intensive fields, require a certain level of physical fitness. This could be assessed through a Physical Fitness Test.

3. Medical Fitness: Medical examinations are carried out to ensure the recruit has no health issues that could prevent them from performing certain jobs.

4. Availability of positions: The availability of certain MOSs can change based on the needs of the military. If there's a high demand for a certain role, those who qualify are more likely to be assigned that MOS.

5. Personal Interest and Skills: While the military's needs take precedence, a recruit's existing skills and personal interests are also taken into account.

Once assigned an MOS, the recruit will receive specific training for that job after completion of their basic training. This is known as Advanced Individual Training (AIT) for the Army and Marine Occupational Specialty School in the Marines.

It's also important to note that while an individual's MOS dictates their main role within the military, soldiers and marines are expected to be able to step into different roles, if necessary, especially in combat situations.

Remember, each branch has its own variation of the MOS system and may use different nomenclature, but the principle remains the same. Please check with military recruiters or liaison officers for more specific information for each branch.