Experimental engines were developed as alternatives for high performance aircraft such as the H-24 configuration Rolls-Royce Eagle 22,[6] the two-stroke Rolls-Royce Crecy[7] and the Rolls-Royce Pennine[8] and Rolls-Royce Exe, the Exe being the only one of these last three engines to fly.[9] However the successful development of the Merlin and Griffon, and the introduction of jet engines precluded significant production of these types.