Veterans eligible for benefits based on exposure to Mustard Gas are those exposed during which of the following?

Veterans eligible for benefits based on exposure to Mustard Gas are specifically those who were exposed during field or chamber testing. This type of exposure refers to the controlled environments where military personnel were tested on the effectiveness and impact of chemical agents, including Mustard Gas. The exposure during these tests is officially recognized as a valid basis for establishing eligibility for certain benefits, as it directly relates to the military's documented testing programs.

In contrast to the other scenarios provided, exposure during basic training, wartime operations, or administrative roles does not qualify as a recognized basis for benefits related to Mustard Gas. While these settings may involve various hazardous conditions, they do not entail the specific and documented exposure to Mustard Gas that occurred during testing phases. Hence, the focus on field or chamber testing is critical for establishing a clear connection between service, exposure, and eligibility for benefits.