What is a tanker in the context of wildland firefighting?

In the context of wildland firefighting, a tanker refers primarily to a fixed-wing aircraft designed specifically for dropping water or fire retardant on wildfires. These aircraft play a crucial role in fire suppression efforts by providing aerial support, allowing for rapid application of large quantities of firefighting substances from the air to help control and extinguish wildfires. The use of tankers enables firefighters on the ground to tackle the fire more effectively, especially in hard-to-reach areas where ground access may be limited.

The other options describe equipment or vehicles used in firefighting but do not align with the term "tanker" as it is commonly understood in this context. For instance, while ground vehicles designed for water transport do exist, they are not classified as tankers in aerial firefighting. Similarly, although units for storing firefighting foam and portable tanks for containing water are essential components of firefighting operations, they do not fulfill the specific role of an aerial tanker in combating wildfires from the sky.