When Soviet submarine, B-59, is discovered "practice depth charges" are dropped; nearly inciting a nuclear war.

February 1945. Below icy Norwegian waters HMS Venturer stalks German U-Boat 864 in a rare WWII submarine attack where both subs operate submerged.

It's 1941, and German Gen. Erwin Rommel and his armies hope to take Egypt, gain control of the Suez Canal, and prevent Britain from receiving vital supplies from the colony of India and the Middle East. The Allies' last line of defense is a fleet of small, British Royal Navy U-class subs stationed on the tiny island of Malta. Despite unpredictable weather and a broken gyrocompass, HMS Upholder and its Lieutenant-Commander Malcolm Wanklyn hunt Italian supply ships to hold the line against the Axis powers and turn the tide of the North African Campaign.

In January 1944, the U-515, commanded by Werner Henke, defies the odds and escapes both Allied depth charges and aircraft to sink ships and return to port despite severe damage. Ten weeks later, the German U-Boat is put to the ultimate test. In April 1944, U-515 heads to the African Gold Coast, where it is tested by one of the new Hunter Killer Groups led by Captain Daniel Gallery.

June 1945. With Japanese merchant shipping slowed to a trickle, US Medal of Honor Recipient, Commander Eugene Fluckey plots to destroy shore based targets along Japan's coast - a campaign that develops unprecedented tactics.

USS Silversides battles depth charges, a jammed torpedo and an emergency appendectomy deep in enemy waters whilst intercepting Japanese ships to Guadalcanal.