Captain Oscar John Lohr stands tense by the small radio station aboard his merchant ship, ears straining for the faintest crackle. He’s waiting for some sign of hope, some message to break the silence that’s hung over the convoy for days. It’s May 1943, and Allied Enigma decrypt machines have gone dark, leaving ships blind, plunging through the gale-force winds of the North Atlantic without knowing if enemy U-boats are out there, waiting beneath the icy waves to strike.The answer finally arrives. The ship bucks violently as a torpedo slams into the starboard side. Steel beams split in half. Hatches explode outward, the ballast ruptures, sending seawater gushing in. The explosion tears through the dawn with a deafening roar, flinging water, debris, and fire into the air. The ship begins to tilt as smoke pours from below deck. They’ve been found.An escort destroyer surges toward the crippled vessel just as the convoy’s communications tracker starts crackling. The sailors’ hearts sink as they decipher the message: A wolf pack is closing in from every direction, ready to send over 40 Allied ships to the bottom of the ocean.Lifeboats hit the waves, and the convoy struggles to reform. The first shapes appear on the horizon: the unmistakable shadows of periscopes, slicing through the surface like sharks ready to feast…