Sabu was first choice to play Gunga Din; when it became clear he was unavailable, Sam Jaffe was hired in his place. In an interview years later, Jaffe (a Jewish Russian-American) was asked how he so convincingly played an Indian Muslim. Jaffe replied he kept telling himself to "Think Sabu."
The "bridge over the deep chasm" scene, in which Annie the elephant shakes a rope bridge while Cutter and Gunga Din are trying to cross it, was actually filmed on a bridge just eight feet off the ground. The background was a realistic painting of a chasm.
Upon release a campaign was launched by the Indian magazine "Filmindia" against the misrepresentation of Indian caricatures in the film, and the displaying of insensitivity towards Hindu customs. Following riots in India and Malaya the film was withdrawn by the censors.
Bits and pieces of the film's use of Lone Pine's boulder-strewn area remain, including the anchors for the rope bridge across the "chasm". Some judicious referencing of the film, and stills from it, make for an interesting tour of the area to locate where a number of the scenes were shot.
In March 1939, the Kipling family objected to a reporter being called Rudyard Kipling, prompting RKO to eliminate that scene from the film when it was re-released. However, it is in the prints available today. The scheduled release date of December 1938 was postponed for retakes. John Sturges, an uncredited editor on this film, directed the remake, Sergeants 3 (1962).
Kelly Reilly had long wanted to make "Gunga Din," and in 1936 brought in Howard Hawks to develop the project. Hawks felt Robert Donat or Ronald Colman were the best choices for the lead with Spencer Tracy as second lead, and early in 1937 he considered Ray Milland and Franchot Tone. However when Hawks took too much time on Bringing Up Baby (1938) he was taken off the project. It's also been said that Hawks was dropped from the film because "Baby" ended up as a box-office bomb, even though it has survived as a comedy classic.
In some prints, the actor playing Rudyard Kipling, has been replaced on one side of the screen by a rather shaky matte when the last lines of poem "Gunga Din" are read. The change was made because of objections from the Kipling family.