revision preference src: The M39 series evolved into the M809 (G908) series in 1969, which followed, but did not replace, it. The M809 Series was then improved into the M939 series. <SEP> tgt: The M39 series evolved into the M809 (G908) series in 1969, which followed, but did not replace, it. The M809 was then improved into the M939 series.