Thus began the smoke-free project; old steam locomotives produced during the Meiji/Taisho periods and large-size steam locomotives for the trunk line were first replaced followed by middle-size for local lines and small-size for branch lines.
こうして始まった無煙化計画は、まず明治・大正時代製の古豪蒸機と幹線用の大型蒸機から始まり、次いで地方線区を走る中型蒸機と支線区用の小型蒸機を置き換えていった。