Probably a "supporting firefighter group vehicle“ to be exact.
Edit: this word is kind of bizarre, because it is a composition of 3 compound words which each are compound words themselves.
Hilfe-leistung (Help Giving = Support) Lösch-Gruppe (Extinguishing Group = Firefighters) Fahr-zeug (Drive Thing = Vehicle)
Hilfeleistungs-Löschgruppen-Fahrzeug is a very odd composite word for Germans too. It’s not commonly used, this is probably "Amtsdeutsch“, a bureaucratic way of naming things as accurately as possible. Mostly used like that by government institutions and Microsoft help documents in german.
See also: Umschaltfeststelltaste (Caps Lock) und Gruppenrichtlinienbearbeitungsprogramm (Group policy Editor).
Shudders. This is why I (as a native German speaker) prefer english documentation.
Could you elaborate on that?