He went to the front with his father to fight in the Battle of Nagashino in May of 1575, and augmented the force under command of Tadatsugu SAKAI that was attacking Mt. Tobinosu; however, as Ietada's father died on the battlefield, he had to succeed to the leadership of the family in his 21st year.
天正3年（1575年）5月の長篠の戦いには父とともに従軍、酒井忠次率いる鳶巣山攻撃軍に加わったが、ここで父が戦死したために数え21歳で家督を引き継いだ。