When Flint 'relaxes' (suspending his body supported only by two chairs: one under his head and one under his heels - the rest, with no support), it was not a special effects shot; James Coburn was able to do so, and it was incorporated into the script.
The safe door locking bars, which Flint easily melts, were cast from "Woods metal", an alloy whose melting point is only 158º F, so low it can be melted in boiling water.
The dock at Galaxy Island and the submarine deck are the same one used as the Nelson Institute in Voyage to the Bottom of the Sea (1964).
On the official studio soundtrack album, the song 'Galaxy a Go-Go' was written by a young Randy Newman, who is in fact the nephew of Lionel Newman, the head of "20th Century-Fox's" Music Department at that time.
When the computers analyze the requirements for an agent to solve the crisis, the end result is simply a blank punched card that has Derek Flint's name typed on it but has no holes punched, rendering it useless for input or output. This one flaw mars a sequence that was otherwise remarkably un-dumbed down for a popular movie of the era. After Cramden asks the world representatives to write down their specifications for the perfect agent, it would not have been surprising to see him feeding a sheet of paper with their handwritten instructions into a slot in a prop "computer". Instead the film shows the information being punched onto cards with real keypunches, the cards put in stacks and loaded into real card hoppers (the origin of the phrase "loading data"), from which they are input and processed by the computer. This was state of the art data processing in 1965.
James Brolin: uncredited as a technician in the background on the villain's submarine. The first time is for just 7 seconds, only 50 seconds into the movie. He appears again at around 1 hour and 5 minutes.