Military munitions that were used, but fail to function as intended are called UXO or unexploded ordnance. Military munitions abandoned without proper disposal or removed from storage in a military magazine or other storage area for the purpose of disposal are called discarded military munitions or DMM. The United States has always maintained a trained and ready military to protect its national interests. As a result of the munitions-related activities (e.g., live-fire training and testing, disposal operations) required to maintain this force, and other actions (e.g., souvenir collecting), UXO or DMM can be found almost anywhere.

Although the Military controls access to areas known or suspected to contain UXO on active installations, a number of areas that are known or suspected to contain military munitions that were once used by the military have been transferred to public uses.

When anyone encounters or believes they may have encountered a munition, they should consider it extremely dangerous. To protect their family, friends and neighbors, everyone should learn and follow the 3Rs of explosives safety: Recognize-when you may have encountered a munition and the potential danger; Retreat-do not touch, move or disturb it; Report-notify local law enforcement of what you saw and where you saw it.

Some situations and items are of special interest. Additional information on chemical agent identification sets (CAIS) and fighting fires in areas encumbered with munitions is presented here.