Troops experience symptoms of a chemical agent exposure. Some US Air Force and Marine units in Operation Desert Storm used color codes to supplement MOPP levels. These codes generally referred to the immediacy of the chemical threat. Enemy forces have the capability to employ NBC weapons, but attack is not probable at this time. Attack probable, units maintain MOPP-0.
Attack is imminent.
Units go to MOPP-4. Attack is probable. Wear CPE and field gear as directed. Attack is imminent or in progress. NBC contamination is suspected or actual.