A five man submarine plants sensors around the worlds oceans to monitor for a impending earthquake.
| Actor | Role |
|---|---|
 Lloyd BridgesDr. Doug Standish | Dr. Doug Standish |
 Brian KellyDr. Craig Mosby | Dr. Craig Mosby |
 Shirley EatonDr. Margaret E. 'Maggie' Hanford | Dr. Margaret E. 'Maggie' Hanford |
 David McCallumDr. Philip Volker | Dr. Philip Volker |
 Keenan WynnHank Stahl | Hank Stahl |
 Marshall ThompsonDr. Orin Hillyard | Dr. Orin Hillyard |
 Gary MerrillDr. August 'Gus' Boren | Dr. August 'Gus' Boren |
 Ron HayesBrinkman | Brinkman |
| GGeorge ShibataProf. Uji Hamaru | Prof. Uji Hamaru |
| DDonald LintonVice President | Vice President |
| FFrank LoganCaptain of the Diligence | Captain of the Diligence |
| DDon WellsSonar Man on the Dilligence | Sonar Man on the Dilligence |
 Celeste YarnallSecretary | Secretary |