Quint
One apparatus carrying the five functions of both an engine and an aerial: pump, tank, hose, ground ladders and an aerial device.
A quint is named for carrying five things at once: pump, water tank, hose, ground ladders and an aerial device. In principle it replaces two apparatus with one.
The appeal is obvious to a budget and contested inside the fire service. One vehicle and one crew instead of two is a real saving; the counter-argument is that a single unit cannot do engine work and truck work simultaneously, so a department running quints has made a staffing and tactical decision as much as a purchasing one.
A fleet manager should treat a quint proposal as a fire operations question with a fleet consequence rather than the reverse. What is clear on the fleet side: a quint is heavy, complex and expensive to maintain, and consolidating two units into one concentrates risk. When it is out of service, both capabilities are gone.