Lt. Commander Mike Dahlgren skippers the S-33, a vintage U.S. WWI submarine which is older than most of its crew. Even though the vessel is considered primitive and suffers numerous defects, it is a deadly tool in the right hands. Now it is being given the chance to prove its worth yet again, as the Americans enter World War II. Lt. Andrew Tyler is the executive officer under Dahlgren. Having just been passed over for an advancement which would have put him in command of his own submarine, Tyler boards the craft, his duty taking precedence over his pride. There, he is joined by fellow officers Lt. Pete Emmett and Ensign Larson. The enlisted men aboard the S-33 include Chief Klough, radioman Wentz, the cook Eddie, Trigger, Mazzola, Tank, Griggs and Rabbit. All ordinary men, some barely out of high school, these sailors are about to embark on a mission more dangerous and frightening then anything they could ever have imagined, but one which has the power to turn the tide of battle. Per the Admiral's command, Lt. Hirsch is taking charge of the S-33 with Marine Major Coonan. Their luggage is a large load of crates with unknown contents, contents which cannot be revealed until the submarine has cleared American waters. Once the S-33 is at sea, the mission is divulged. Like the Trojan horse of Greek mythology, their craft has been rigged to resemble a U-boat, the notorious Nazi submarine which traversed the depths of the North Atlantic. They are to rendezvous with what Lt. Hirsch assumes is a stranded German submarine, posing as Germans and capture the Enigma' machine, a valuable top-secret coding device that could help the Allies stop the incessant attacks of the deadly wolfpacks at sea. The mission must be conducted in total secrecy, as seizing this device without the enemy's knowledge is the only way for Allied intelligence to decipher their movements and put an end to the enormous losses inflicted upon convoys carrying vital supplies across the ocean. If all goes as planned, they will destroy the U-boat, take the prisoners back to the United States and the enemy will never know about their secret acquisition. Following an unexpected turn of events, this group of American sailors become trapped in the enemy's vessel, deep in hostile waters, and at a major disadvantage as to how to operate the foreign sub. The destiny of these nine ordinary men, as well as the fate of their mission, will ultimately depend on their camaraderie, their instinct, their battle against time and a battle against their own fears.