What is the primary purpose of a mounted deck gun on a fire engine?

The primary purpose of a mounted deck gun on a fire engine is to deliver large volumes of water to a fire. This specialized equipment allows firefighters to apply significant amounts of water quickly and efficiently from a stable platform, which is crucial during firefighting operations, especially in large fires or in situations where rapid suppression is necessary. The deck gun can often be operated remotely, allowing the crew to position it for optimal coverage without needing to be at the nozzle, thereby increasing safety for the firefighters on scene.

In contrast, the other options describe functions that do not align with the primary function of a deck gun. Storing firefighting chemicals is more related to other equipment or compartments on the fire engine designed for that purpose. A mounted deck gun does not serve as a communication device, which is typically provided by radios or other communication technology. Finally, while maintenance of the fire engine is critical for operational readiness, it is not the role of the deck gun, which is focused solely on water delivery during firefighting efforts.