Cooper played a United States Navy physician, Lt. Charles W. "Chick" Hennesey, with Abby Dalton as Navy nurse Lt. Martha Hale. In the story line, they are assigned to the hospital at the U.S. Naval Station in San Diego, California.
- Jackie Cooper as Lt. (later Lt. Commander) Charles "Chick" Hennesey, M.D.
- Abby Dalton as Lt (JG) Martha Hale, R.N.
- Roscoe Karns as Capt. (later Rear Admiral) Walter Shafer
- Henry Kulky as Chief Petty Officer Max Bronski
- James Komack as Harvey Spencer Blair, III, D.D.S.
- Arte Johnson as Seaman Shatz
- Herb Ellis as Dr. Dan Wagner
- Robert Gist as Dr. Owen King
- Stephen Roberts as Commander Wilker
- Harry Holcombe as William Hale
- Ted Fish as Chief Branman
- Frank Gorshin as Seaman Pulaski
- Norman Alden also as Seaman Pulaski
Actor and singer Bobby Darin was cast in the second episode (October 5, 1959) with the unlikely name of "Honeyboy Jones". Less than a year earlier, Darin had rocketed to fame with his version of the song, "Mack the Knife".
Prior to being cast as Opie Taylor on The Andy Griffith Show, child actor Ron Howard played "Walker", a little boy temporarily left in Hennesey's care in the 1959 episode "The Baby Sitter". Gary Hunley, another child actor, appeared in the same episode.
Charles Bronson, en route to a long film career, was cast twice as Lt. Cmdr. Steve Ogrodowski, a Navy intelligence officer.
Other guest stars: