What action can be taken to reduce the effects of hydrogen chloride gas?

The action that effectively reduces the effects of hydrogen chloride gas involves positioning soldiers upwind of the artillery. This is crucial because hydrogen chloride gas is heavier than air and can travel along the ground. By staying upwind, soldiers remain in a safer location where the gas is less likely to reach them, minimizing their exposure to the harmful effects of the gas.

It is important to understand that while other measures, such as providing ventilation in closed spaces or wearing protective masks, can offer some protection or alleviation from exposure, the most effective immediate action is to avoid the gas entirely by positioning oneself upwind. This strategy leverages the natural dispersion of the gas, ensuring a lower risk of inhalation and other health risks associated with hydrogen chloride exposure.