 Tim HoltLt. Cmdr. John 'Twill' Twillinger | Lt. Cmdr. John 'Twill' Twillinger |
 Audrey DaltonGail MacKenzie | Gail MacKenzie |
 Hans ConriedDr. Jess Rogers | Dr. Jess Rogers |
 Barbara DarrowJody Simms | Jody Simms |
 Max ShowalterDr. Tad Johns | Dr. Tad Johns |
| HHarlan WardeLt. Robert 'Clem' Clemens | Lt. Robert 'Clem' Clemens |
 Gordon JonesSheriff Josh Peters | Sheriff Josh Peters |
 Mimi GibsonSandy MacKenzie | Sandy MacKenzie |
 Marjorie StappConnie Blake | Connie Blake |
 Jody McCreaSeaman Fred Johnson | Seaman Fred Johnson |
 Wallace EarlSally | Sally |
| DDennis McCarthyGeorge Blake (lab assistant) | George Blake (lab assistant) |
 Sarah SelbyMrs. Simms | Mrs. Simms |
 Milton ParsonsLewis Clark Dobbs | Lewis Clark Dobbs |
 Charles TannenSeaman Wyatt (Radioman) | Seaman Wyatt (Radioman) |
| RRobert BenevidesSeaman Morty Beatty | Seaman Morty Beatty |
| JJohn CarlyleMonster Victim | Monster Victim |
| JJohn CloseDeputy Larry | Deputy Larry |
 William ForrestAdmiral Greenhouse | Admiral Greenhouse |
| GGil FryeDeputy Scotty | Deputy Scotty |
 Joseph HamiltonOther Lock Watchman | Other Lock Watchman |
 Charles HerbertBoy with Morty's Cap | Boy with Morty's Cap |
 Byron KaneCoroner Nate Brown | Coroner Nate Brown |
| RRalph LittlefieldGatekeeper | Gatekeeper |
 David McMahonPatterson | Patterson |
 Ralph MoodyWatchman at Lock 57 | Watchman at Lock 57 |
 William SwanSeaman Howard Sanders | Seaman Howard Sanders |
| HHal TaggartDavis - Resort Owner | Davis - Resort Owner |
 Mack WilliamsCaptain Masters | Captain Masters |
| DDan GachmanDeputy Brewer | Deputy Brewer |
