A compressed air / foam fire fighting system which is sufficiently compact to be carried on the bed of a pick-up truck includes a water tank, a pump for providing water at substantial pressure to a water conduit, an engine for driving the pump, a foam reservoir including a bladder tank connected to the pump, an air compressor, an engine for driving the air compressor, a differential pressure valve connected in the water conduit, a metering valve adjustable to supply a desired proportion of foam concentrate to water connected across the differential pressure valve, an air valve for controlling the amount of air from said compressor, and an air injection venturi for mixing air into a water / foam concentrate. A two-way valve connected between the tank and the pump is movable between a first position where water is pumped from the water tank and a second or suction position where water is drawn from an outside tank or other source. The system can supply plain water, a water / foam mixture, a mixture of compressed air, water, and foam, or compressed air only.