The wolfpack tactic was made famous by Admiral Karl Dönitz, Hitler's mastermind of submariners. His strategy: to send teams of U-boats to bear against the convoys of ships heading from Canada to Britain, cut maritime lifelines, and starve the enemy into defeat. Take a deep dive into the North Atlantic as we go above and below sea level to relive one of the first attacks of Dönitz's lethal subs in 1940, headed by leader of the pack Commander Otto Kretschmer. Then follow Britain's war strategists as they race to combat this new deadly attack.

December 1941-following the Japanese assault on Pearl Harbor, five Nazi U-boats set out on a secret mission to attack ships off the shores of the United States to thwart the American war effort.

January 1943. America's submarine force struggles to gain an edge in the South Pacific. Dudley Mush Morton, Commander of USS Wahoo, sets out to turn the tide. The new skipper decides to take on an entire convoy. If he succeeds, he will be the first American submarine commander to claim such a prize.

March 1943. Two Allied convoys, HX.229 and SC.122 leave North America bound for Britain. They total nearly 100 ships carrying vital food and raw materials to supply the Allied war effort. John Gordon Luther commands the short-handed escort group charged with protecting convoy HX.229. Short at least two ships, he lacks adequate defenses for the mid-Atlantic U-boat attack that the Karl Donitz, Gross Admiral of the German Navy, has in store for them. For three days the convoys are hammered by a merciless litany of torpedo attacks and an Atlantic winter storm. Many ships are hit and Luther is repeatedly torn between protecting the convoy or falling back to rescue survivors of torpedoed ships. It's the largest convoy battle of the Second World War and one that nearly costs the Allies the Battle of the Atlantic.

June, 1944. Six allied commandos spying on Japanese ship movement fall under threat when their covert operation is discovered by the enemy. Stuck in the jungles of occupied Borneo, the only hope for rescuing them is USS Harder, an American Gato Class submarine. To save the operatives, Commander Sam Dealey and his crew ply through waters guarded by a key Japanese Naval base, an act that pits the single submarine against dozens of warships. The daring rescue puts USS Harder's strength and stealth to the test.

December, 1943. Fueled by the loss of mentor and friend Dudley Mush Morton, Richard Hetherington O'Kane and his submarine USS Tang set out to assault Japanese shipping. In four patrols O'Kane rises to the ranks of America's top submarine commander. But in the Formosa Strait his last Mark 18 torpedo turns against him. As O'Kane's submarine meets its end, an unforgettable fight to survive begins.