The Bullfinch was a parasol-winged single-seat fighter which strangely was designed in such a way by Frank Barnwell that it could be changed into a two-seat sesquiplane reconnaissance fighter with a stretched fuselage and a bottom wing nailed on. It was an early application of the Jupiter engine, which Bristol took over from Cosmos Engineering. The third and last Bullfinch I monoplane was converted to the sole Bullfinch II biplane and first flew as such on 17 March 1924.