Jack Lord lived in Beverly Hills when he was asked at the last minute to read for the part of McGarrett. He read for it on Wednesday, flew to Hawaii on Friday, and was in front of the cameras the following Monday. He later became a permanent resident and prominent figure in Hawaii, contributing to many local causes and charities, and often mentioned publicly in consideration for political office. After he died, the state erected a statue of him.
Magnum, P.I. (1980) began production soon after this series wrapped its last episode. Early episodes included references to this show, but a plan to have Jack Lord appear as McGarrett never came to pass.
Jack Lord was the only cast member to stay with the series during its entire 12-year run. Zulu , the first of the regular cast to depart the show, left in the 4th season. Kam Fong left after the 10th season. James MacArthur left the series after Season 11. In a 1996 interview, he revealed that he had become tired, and wanted to do other things. It was also reported that there were delays in the decision to renew the show for another season, and James MacArthur took another job that was offered.
The hula dancer in the opening montage is Helen Torco, in an uncredited role. Known professionally as Helen Kuoha-Turco, she was later a professor at Windward Community College. She had a credited role in an episode of the rebooted Hawaii Five-0 (2010). Until 2015, those were Torco's only acting credits.
This was the longest-running crime show in television history until Law & Order (1990)'s 13th season, 2002-2003. It can be considered the second-longest running crime show if Gunsmoke (1955) isn't considered a crime show. Law & Order: Special Victims Unit (1999) hit its 13th season in 2011-2012, and the original "Law & Order" (1990)_ ran for 20 years, so it could also be considered the third-longest running crime show.
McGarrett's office was in Iolani Palace, the actual palace used by the last kings and queens of Hawaii. In 1969, the Palace had fallen into disrepair after years of abuse and neglect. it has since been restored, and the palace can now be toured for $20.
The "Five-O" in the series' title pertains to Hawaii as the 50th state to enter the union (August 21, 1959), even though the "O" in the title is not the number zero (0). The meaning is the same, in the 2010 reboot, but the "0" in the title is the number zero (0).
The opening montage consists of: a breaking wave (from the film Surfari (1967)), a hula dancer (Helen Torco), the "Lady Columbia" statue at the National Cemetery of the Pacific, model Elizabeth Logue running down the beach, a close-up of Ms. Logue from a side view, 13-year-old local resident Mel Kinney, Elizabeth Logue turning toward camera, red neon sign (formerly the Tops restaurant in Waikiki Diamond Head), flashing blue light, the Aloha Tower, Honolulu, and the Ilikai Hotel.
McGarrett was a Navy Intelligence officer, with the rank of Lieutenant Commander, before he became head of Five-O. He ostensibly remained in the U.S. Navy Reserves throughout the series, occasionally recalled to active duty to assist the Navy or Coast Guard on special cases.
For the ninth season, the Five-O offices moved out of the Iolani Palace and into an office building down the street, partly because the Iolani Palace was getting a facelift, and partly because CBS was building a new studio for the series, which wasn't ready in time for the early episodes. The Five-O office scenes were filmed in the office building, which was introduced in each episode that season by showing the Iolani Palace with scaffolding over its facing, then quickly panning down the street to the office building. Sometimes an exterior shot of the office building would show McGarrett pacing in front of his "new" office window. They moved back for the tenth season.
Following the death of Leonard Freeman in 1974, Jack Lord stepped into Freeman's shoes and ran most of the production for the remainder of the series, although he was never credited on screen as a producers. This was by agreement from 1974-1980, in exchange for Lord's shared ownership, with the Freeman estate, of episodes produced between Freeman's January 1974 death and the end of the series in 1980. Prior to this agreement, Lord nearly walked off the series in 1974, after a dispute with CBS.
Other than Wo Fat, other notable adversaries for McGarrett that appeared in more than one episode included mob bosses Honore Vaschon and Tony Alika, pimp Big Chicken, and the Robin Hood-like Lewis Avery Filer.
Al Harrington and Herman Wedemeyer both appeared in different roles on the show before assuming the roles of Ben and Duke respectively. Wedemeyer was in the very first episode playing Honolulu police Lt. Balta.
In many American inner city neighborhoods, "Five-O" is one of the many slang terms for the police. "Five-0" (spelled differently, sounds the same) is also a slang term for the Ford 302 engine option in the Ford Mustang automobile. In the photography world, "Five-0" is slang for a 50mm focal-length lens (also called a Nifty Fifty), and two mid-2000s era DSLR cameras, the Nikon D50 and Canon 50D.
Jack Lord was not in a key shootout scene because it was filmed on a Saturday, and, according to the producers during a special feature in season two of the new 2010 series, Jack Lord, contractually, never worked on Saturdays.
It was disclosed in "Good Night, Baby - Time to Die!" (s4, ep21) that McGarrett had been hired by The Governor in 1959, immediately upon Hawaii's creation as the 50th state, as head of Five-O, and that McGarrett took no vacation time off between 1959 and 1968, when McGarrett "was tired" and visited Switzerland to rest.