The U.S. submarine Anthony Wayne is underway for a top-secret mission. Onboard is a highly classified device that will give the Americans a decided nuclear advantage. The entire mission and the secret technology are threatened when the sub commander discovers his crew has been infiltrated by enemy agents. The commander is charged with trying to protect the device while ferreting out the enemy agents. Compounding matters is the state of the commander's physical and mental condition, which is being questioned by his crew.
| Actor | Role |
|---|---|
 Joseph CottenAdmiral | Admiral |
 Lloyd HaynesLt. Dave Burston | Lt. Dave Burston |
 Dewey MartinSkip Langley | Skip Langley |
 Leonard NimoyComdr. Phil Kettenring | Comdr. Phil Kettenring |
 William WindomCapt. Frank Reardon | Capt. Frank Reardon |
 Keenan WynnOrville Kelly | Orville Kelly |
 Malachi ThroneDr. Dykers | Dr. Dykers |
 Sam ElliottEns. William 'Bill' Sandover | Ens. William 'Bill' Sandover |
 Ivor BarryDonald Ellington | Donald Ellington |
 Ron MasakCPO Corky Schmidt | CPO Corky Schmidt |
| GGordon HobanSecond Karp (False Karp) | Second Karp (False Karp) |
| LLee StanleyLt. Manners | Lt. Manners |
| DDavid ThorpeLt. Benson | Lt. Benson |
| HHenry OlekCab Driver | Cab Driver |
| DDale TarterClarence W. "CW" Karp (First Karp) | Clarence W. "CW" Karp (First Karp) |
| JJames BeachRadar Operator | Radar Operator |
 John WinstonEnglish Scientist | English Scientist |
 Larry McCormickRadio Operator | Radio Operator |
| PPaul SearsPaine | Paine |
| EEllen TuckerMrs. Karp | Mrs. Karp |
| BBill KellerShore Patrolman | Shore Patrolman |
 Bobby HerbeckSonarman | Sonarman |
| BBo JohnsonSeaman | Seaman |