Tim Holt

Character: Lt. Cmdr. John 'Twill' Twillinger

Audrey Dalton

Character: Gail MacKenzie

Hans Conried

Character: Dr. Jess Rogers

Barbara Darrow

Character: Jody Simms

Max Showalter

Character: Dr. Tad Johns

Harlan Warde

Character: Lt. Robert 'Clem' Clemens

Gordon Jones

Character: Sheriff Josh Peters

Mimi Gibson

Character: Sandy MacKenzie

Marjorie Stapp

Character: Connie Blake

Jody McCrea

Character: Seaman Fred Johnson

Wallace Earl

Character: Sally

Dennis McCarthy

Character: George Blake (lab assistant)

Sarah Selby

Character: Mrs. Simms

Milton Parsons

Character: Lewis Clark Dobbs

Charles Tannen

Character: Seaman Wyatt (Radioman)

Robert Benevides

Character: Seaman Morty Beatty

John Carlyle

Character: Monster Victim

John Close

Character: Deputy Larry

William Forrest

Character: Admiral Greenhouse

Gil Frye

Character: Deputy Scotty

Joseph Hamilton

Character: Other Lock Watchman

Charles Herbert

Character: Boy with Morty's Cap

Byron Kane

Character: Coroner Nate Brown

Ralph Littlefield

Character: Gatekeeper

David McMahon

Character: Patterson

Ralph Moody

Character: Watchman at Lock 57

William Swan

Character: Seaman Howard Sanders

Hal Taggart

Character: Davis - Resort Owner

Mack Williams

Character: Captain Masters

Dan Gachman

Character: Deputy Brewer

Michael Dugan

Character: Clarke