Kunshiro Kiyozumi is a small man with gray hair and a stooped back who lives alone and still pedals his bicycle to the supermarket. At 97, he cuts an unprepossessing figure to the younger shoppers busy texting while filling their carts, unaware that his life contains a dramatic story shaped by history’s deadliest war.

At age 15, Kiyozumi became the youngest sailor aboard the I-58, an attack submarine of the Imperial Japanese navy. In the closing days of World War II, it prowled the Pacific Ocean, torpedoing six Allied ships, including the heavy cruiser USS Indianapolis, which it sank.

He served in a military that committed atrocities in a march across Asia, as Japan fought in a brutal global conflict that was brought to an end with the atomic bombings of two of its cities. All told, World War II killed at least 60 million people worldwide.