During the Third Shinobi World War, a dear friend of Fugaku died in battle causing him to unlock the mangekyou sharingan. At the end of the Third Shinobi World War, Shisui witnessed his best friend die, also awakening the Mangekyō Sharingan. It was stated directly in the anime for fugaku, and in the Itachi Shinden novel for Shisui.And like i said neither of them was said to have awakened Sharingan during that war. Not even Fugaku.