Maruyu  

, まるゆ

Maruyu is a distinctive submarine that was created and operated by the Imperial Japanese Army. It has a name derived from the circle "〇," which means "Maru" in Japanese, and the hiragana character "ゆ," meaning "yu." The symbol inside the circle resembles a fish swimming in a bowl, fitting for a submarine. Using Maruyu as a material during modernization can bring good fortune. The Kai version offers even more luck.