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

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.