MOS 31B refers to the United States Military Police. This position is tasked with the enforcement of military laws and regulations as well as with general safety on Army installations. Military Police also play a support role on an active battlefield, with a focus on security and police intelligence.
As of 2014, a candidate for the MOS 31B position must earn a score of 91 in the skilled technical area on the Armed Services Vocational Aptitude Battery test and must possess a security clearance ranking of "Confidential." Another requirement of the position is the physical strength to carry out moderately heavy tasks, such as suspect restraint and crowd control.