On Her Majesty's Secret Service was originally intended as the next Bond film after Thunderball, but producers switched to You Only Live Twice because OHMSS would have required searching for high, snowy locations.
Director Lewis Gilbert initially declined to direct the film, but accepted after producer Albert R. Broccoli told him he couldn't give up a job with 'the largest audience in the world'.
The location-scouting team, including director Lewis Gilbert, cinematographer Freddie Young, producers Broccoli and Harry Saltzman, and designer Ken Adam, cancelled their booked return flight to the UK (BOAC Flight 911) to watch a ninja demonstration; that flight crashed 25 minutes after takeoff, killing everyone aboard.
SPECTRE's headquarters was changed from a seaside fortress to an extinct volcano after the filmmakers learned the Japanese do not build castles by the sea.
Editor Peter R. Hunt, who had wanted to direct the film but was turned down, was found on holiday in Tokyo by the crew and was instead hired to direct the second unit.
The original novel's early screenplay draft by Sydney Boehm closely followed Ian Fleming's book, but the producers brought in Harold Jack Bloom to rework the story in Japan; though his script was rejected, elements like Bond's fake death and burial at sea and the ninja attack were kept, earning him an 'Additional Story Material' credit.
Screenwriter Roald Dahl, a close friend of Ian Fleming with no prior screenwriting experience, called the source novel 'Fleming's worst book, with no plot in it which would even make a movie' and said he could only retain four or five ideas from it, largely inventing a new plot inspired by a missing nuclear bomber incident over Spain and the Soviet and American first spacewalks.
Jan Werich was originally cast as Blofeld, but after producers felt he resembled a 'poor, benevolent Father Christmas' and wasn't menacing enough, he was replaced mid-shoot by Donald Pleasence, who developed the character's scar after considering a hump, limp, beard, and lame hand.
Actress Mie Hama was initially cast as Tanaka's assistant but struggled with English and was nearly fired; after co-star Tetsurō Tamba suggested she might commit suicide if dropped, producers instead swapped her role with Akiko Wakabayashi, who had been cast as Kissy.
During filming of the autogyro 'Little Nellie' battling helicopters, cameraman John Jordan's foot was severed by a helicopter's rotor due to downdraft; it was surgically reattached but later amputated in London, and Jordan continued working on the Bond series with a prosthetic foot.
Because the Japanese government would not allow explosions to be filmed in a national park, the crew relocated the volcano climax's explosive shots to Torremolinos, Spain, which was found to resemble the Japanese landscape.
The SPECTRE volcano base set, including a heliport and monorail, was built at Pinewood Studios at a cost of $1 million and stood 45 metres (148 feet) tall, visible from 5 kilometres away, drawing many local spectators.
Nancy Sinatra recorded the title song after her father Frank Sinatra passed on the opportunity; she was reportedly very nervous during recording, at one point wanting to leave the studio and joking she sometimes sounded like Minnie Mouse, with composer John Barry noting the final track used 25 different takes.
A different title song was originally recorded by Julie Rogers but discarded, with only two lines surviving into the final lyrics; another alternative version sung by Lorraine Chandler was later discovered in RCA Records' vaults and became popular on the Northern soul scene.
Sean Connery's then-wife Diane Cilento performed the swimming scenes for at least five Japanese actresses, including Mie Hama.
