Used by the works Lotus team and the privateer Rob Walker Racing Team in 1961, the 21 was the first works Lotus to win a Formula One Grand Prix, in the hands of Innes Ireland at the 1961 United States Grand Prix. (Previous victories were taken by Rob Walker's team). Customer teams continued to use it up to 1965. It was soon rendered obsolete by the Lotus 24 and the monocoque Lotus 25 introduced for the 1962 Formula One season.