Hyakuren Tekka - is a word that was used to describe various hard trainings and battles in which people engage with a fierce struggle, and it was used during the period of militarism, playing on words linked with hyakusen renma (experiencing various battles to become battle-wised).
百錬鉄火-鎬を削るような厳しい訓練や戦闘の数々という意味で、軍国主義にあった時代に、百戦錬磨に掛けて使われた言葉である。