This pop-pop boat No D is similar to the No E & No F, with the addition of a chimney. I don't know how many different pop-pop boats CK made or if any of them are much different.
It is of typical lithographed tin-plate construction with a diaphragm type boiler and twin exhaust pipes. It is candle powered with the burner designed to clip onto the exhaust pipes.
It is in well played-with condition and quite rusty but, as far as I can see, all original.