Magnum was a Vietnam War Veteran. At the time, Vietnam and its aftermath were still controversial. Magnum, T.C., and Rick have been cited as some of the first positive portrayals of Vietnam Veterans on a network TV series.
The show is set in Hawaii partly because CBS did not want to close its Hawaii production offices when Hawaii Five-O (1968) ceased production in 1980. This show started production that year and contains occasional references to Steve McGarrett and Hawaii Five-O (1968), although McGarrett was never shown.
In an interview for "Bravo TV's Countdown of the 100 Greatest Television Characters" Tom Selleck said his character, Thomas Magnum, was initially written as a "James Bond of television, visiting stewardess on each arm, flawlessly perfect" kind of character, which Selleck hated. By his own admission, he told the writers and producers "I'm tired of playing what I look like." When asked what he wanted to do, Selleck remembered how much fun he had working with Jim Garner on The Rockford Files (1974) and suggested making Magnum more of a laid back, blue collar average Joe. His rationale was that if men watched the show and were able to identify with him, it would bring in even more male viewers. THe writers and producers initially refused, and Selleck threatened to do Raiders of the Lost Ark (1981) instead. The writers and producers relented, and backed down, and Magnum became the approachable, charming jock character Selleck would be famous for.
T.C.'s multicolored helicopter for his Island Hopper charter service was a Hughes 500, a commercial variant of the Hughes OH-6 Cayuse developed for the U. S. military. Several different helicopters were used during the series including both D series (T-tail) and C series (Y-tail) variants.
Magnum's Navy uniform includes the blue and white ribbon for the Navy Cross and the Naval Special Warfare insignia. That means he was a SEAL, and earned the nation's second-highest award for naval personnel.
Soon after this show ended, Universal floated the idea of a theatrical film with the original cast.Tom Clancy wrote a script about Magnum returning to the Navy and his subsequent adventures. Universal ultimately felt that the original cast and Clancy's script would not be a big enough draw at the box-office.
Magnum's full name was Lieutenant Thomas Sullivan Magnum IV, USN. The two gold stripes on the shoulder-boards of his dress whites indicate he was a Lieutenant. His father, Commander Thomas Sullivan Magnum III, USN, was a Naval aviator killed in Korea. He appears in flashbacks. His grandfather, Captain Thomas Sullivan Magnum Jr., USN, appears in the 8th season episode "Resolutions." His great-grandfather, Thomas Sullivan Magnum, appears in a home movie that Magnum and his nephew watch in the 6th season episode "Going Home."
Tom Selleck is a big Detroit Tigers baseball fan. Several episodes feature references to the Tigers. When the Tigers won the World Series, CBS made tentative plans to film an episode in the Detroit area.
Higgins has four illegitimate siblings, with same father but different mothers. Father Paddy McGuinness is an Irish priest. Soo Ling is his half-Chinese sister. Elmo Ziller is a rodeo owner from Texas. Don Louis Mongueo is a royal heir to the throne of Costa De Rosa in South America.
The recurring character with the most appearances was Higgins' female companion, Agatha, played Gillian Dobb who had no professional acting experience outside of this show. Like John Hillerman, Dobb was American, but her character was British.
Thomas Magnum's weapon of choice is a Government model Colt 1911 A1 .45 cal. automatic pistol. When the need arises, he usually carries it tucked into the waistband of his pants, otherwise known as "Mexican carry." The Colt 1911 A1 was the standard issue U.S. military pistol during the Vietnam era, so it's reasonable to assume that it was his personal sidearm from his Navy days.
When Magnum's misadventures bring trouble to the Robin Masters Estate, Higgins arms himself with a British Webley Mk-VI .455 caliber revolver. It was a standard British military-issue weapon in both World Wars, so it's reasonable to assume that it was Higgins personal sidearm from his time with the British Army in World War II, especially since Higgins has a deep emotional attachment to the weapon.
Aside from his trademark Detroit Tigers cap, Magnum also wore a US Navy ball cap. The name and logo were those of VM-02, a unit located at Da Nang Air Base, a US military complex located in Vietnam during the war. It's the designation for Marine Corp Helicopter Observation Squadron 02 which, really was based in Da Nang, Republic of Vietnam from 1965 to 1971. T.C. wears that ball cap as well.
Gerald McRaney mentioned in an interview that he auditioned for a role in the pilot episode before being cast in Simon & Simon (1981). McRaney would later appear as his Simon & Simon character in a crossover episode.
John Hillerman was born in 1932. As such, he was 7 years old when World War 2 began and 15 when it ended and too young to have served in the military. He was only 6 years older than Roger E. Mosley, who was born in 1938. Mosley's character TC was said to have graduated college in 1968 and then enlisted in the USMC, however this would have made him age 30 instead of the normal age 22. Even though they were presumed to be about the same age due to their military service at the same time, Mosely was 7 years older than Tom Selleck and 9 years older than Larry Manetti.
The trivia items below may give away important plot points.
Lt. McReynolds was killed off in season 3 because Jeff McKay was cast to co-star in Tales of the Gold Monkey (1982). When that show was canceled after one season, McKay returned to Magnum as Mac's ghost and as con man Jim Bonnick, a Mac look-a-like.
In the background of Higgins' office on the shelf is a model of the famous bridge that the British built in world war two as seen in the movie Bridge on the River Kwai. It is assumed that Higgins was a British POW and helped build the bridge.