Most people use the terms fire engine and fire truck interchangeably, without realising that the two are quite different.
A fire engine is usually the first vehicle to report at the scene of a fire. Fire engines are fitted with a water tank, a pump, and powerful hoses up to thousands of feet long. These fire engines aid the firefighters by fighting the raging flames with flame-repelling chemicals and water. The hundreds of gallons in the tank of a fire engine serve as the source of water for the firefighters till they connect to another external water source. The nozzles for the hoses and other tools are also present in a fire engine.
On the other hand, a fire truck is used to transport firefighting equipment as well as the firefighters. It carries tools like aerial and ground ladders, power equipment, and other rescue gear. The fire trucks do not transport water. Some ladders use the fire truck as a base as they rise upwards.
A few fire engines may carry the ladder as well, but mostly ladders are present in a fire truck.
The firefighters handle the fire situation accordingly. One might see the first response vehicle making no attempt to fight off the flames because their focus at the time may be the rescue of the victims from the blazing fire or arranging roof ventilation, and keeping an eye on the direction of the fire.
Fires are quite unpredictable and can spread rapidly. Thus, support equipment like powerful lights, protective gear, chainsaws, masks, etc. help the firefighters do their job effectively. Thus, the firefighters in the truck work in collaboration with the ones on the fire engine to tackle the raging flames effectively.
Next time you see a red vehicle speeding off to an unknown fire, pay close attention to the details, and you will easily be able to tell a fire engine apart from a fire truck!