MOPP — Mission Oriented Protective Posture — is the U.S. military system for specifying how much chemical, biological, radiological, and nuclear (CBRN) protective equipment personnel must wear in a given threat environment. MOPP levels run from 0 to 4, with each level adding another layer of protection and another layer of heat stress. What It Is MOPP is a tiered readiness framework, not a single piece of equipment. It describes how much of the available CBRN protective gear must be worn, allowing commanders to calibrate the trade-off between protection and operational effectiveness.