5 lb AMEREX 2A-10BC (USCG marine rating Type A Size II/Type BC Size I) dry chemical fire extinguisher.
Only had to use it once, when I was an engineer for the Oceanic Division of Westinghouse Electric Corporation in their Vallejo CA field office. Driving to work one morning on Broadway, a 1970's era Cadillac pulled out in front of me, with more black smoke coming from under the car than you could imagine.
I honked; he waved back. I honked again; he waved again, but this time must have looked in the rear view mirror, because he immediately pulled over and lept out of the car. By this time there were visible flames accompanying the smoke.
As a retired submarine officer, I knew instinctively what to do, but there wasn't anyone around to order to put out the fire. So I grabbed my handy-dandy 5 lb AMEREX 2A-10BC (USCG marine rating Type A Size II/Type BC Size I) dry chemical fire extinguisher. He popped the hood on his Cadillac and - assuming the proper position - I implemented PASS (Pull the pin, Aim, Squeeze the trigger, Sweep) and promptly emptied 5 lbs of dry chemical fire retardant into his engine compartment.
Did absolutely no good.
Fortunately, someone in the nearby Jack-in-the-Box had the presence of mind to call the fire department, who soon arrived, told me to get the heck out of the way, and proceeded to put out the fire in what was left of this guy's Cadillac.
Sic transit gloria...