The black and white opener of "The Battleship Island" focuses on a part of wartime economy rarely seen in film- the support staff. Specifically, the miners, who come up with the raw material that is later purposed into shiny toys for the military. The work is dangerous, especially under the stress of wartime quotas. But it's especially bad for the Korean characters of "The Battleship Island", who labor for the Japanese near the end of the doomed effort that was World War II in the Pacific.
Don't mistake "The Battleship Island" for mere torture porn about how the Japanese Empire was bad. I mean, it was bad, don't get me wrong. Director Ryoo Seung-hwan reminds us that while the men worked in horrible conditions, the women had it even worse- they became comfort women. Rather paradoxically, they were comfort women for the male Korean miners in addition to the Japanese soldiers, because everyone's actions for the war effort were considered, legally at least, to be equal.