We now exist in a time further away from Wolfgang Petersen’s “Das Boot” than that film was to the end of the global conflict it depicted.

Almost four decades since the German submarine-centered epic first arrived in theaters, Hulu and Sky are partnering for a summer release of a new eight-part companion piece to the original story. “Das Boot” picks up a year after the 1981 film (based on the Lothar-Günther Buchheim novel of the same name) leaves off. Instead of solely focusing on underwater life aboard a U-boat, this new Hulu series also looks at life on the shore among the growing French resistance.

The trilingual ensemble — including Lizzy Caplan, Vicky Krieps, Vincent Kartheiser, Tom Wlaschiha, James D’Arcy, and Rick Okon — span across countries and international water, through Nazi-controlled France and the launch of the German fleet’s newest ship, U-612. But alongside the spy subplots taking...