GTA 5 FIRETRUCK ULTIMATE DRIVING SIMULATOR

Live out your childhood dreams in your very own fire truck. It will be worth the effort of hauling it through the streets when you're firing the water cannon, blaring the siren and flashing enough lights to kickstart an impromptu rave. Who cares if the Los Santos Fire Department rejected your applications? Now's your chance.
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— Warstock Cache & Carry description, GTA Online.
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Wikipedia has an article on: Fire engine
The Fire Truck (or Firetruck) is a general purpose firefighting apparatus equipped with a deck-mounted water cannon/deluge gun, appearing in every Grand Theft Auto game. It is manufactured by MTL in the HD Universe.

The Fire Truck is depicted in every appearance as a large truck-based vehicle with a predominantly red paintjob, long chassis and bulky design, evidently to contain firefighting equipment.

2D Universe
Grand Theft Auto features two variants of the Fire Truck, which are generally depicted in the style of typical American fire trucks, though their exact sources of inspiration are unknown:

The first one is a standard cab with a long hood/nose, appearing in Liberty City and Vice City. It has a single light bar and a "FIRE" marking on the roof.
The second one is a cab-over-engine truck, exclusive to San Andreas. It has what seems to be a round red rotating light, a "SAFD" marking and a red stripe on the roof.
The Fire Truck featured in Grand Theft Auto: London 1969 and Grand Theft Auto: London 1961 assumes a more 1960s European design, likely to be based on a chassis of a British truck such as a F/Delta-type Dennis; the vehicle's design is also adapted into the ICBM. It has a white "FIRE" marking, rotating lights and a ladder/ladder-cannon setup.