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Why might a military force use a persistent chemical agent to deny access to an area?

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American soldiers in World War I uniforms, some wearing gas masks, advance with rifles during a simulated gas attack exercise on a rocky battlefield. — chemical weapon American soldiers participating in a simulated gas attack exercise, World War I.

A military force may use persistent chemical agents—such as VX or mustard gas—to neutralize critical infrastructure, including air bases, seaports, or key staging areas, for an extended period. By contaminating these locations, a force can effectively deny their use to an adversary.1

Unlike nonpersistent agents, which evaporate rapidly and are typically employed for temporary effects, persistent agents remain in a lethal form for days or weeks. This tactical application forces the opposing side to either avoid the area entirely or operate under the significant burden of protective gear. Operating in such equipment—including masks, protective overgarments, and specialized gloves—can reduce a military force's conventional combat effectiveness by 25 percent or more due to physical stress, heat buildup, and decreased mobility.12

The use of chemical weapons is prohibited under the Chemical Weapons Convention, as they are classified as weapons of mass destruction that cause indiscriminate harm.3