A common ploy in 1950's sci-fi movies was to show a V-2 or other real rocket taking off in the movie as a surrogate for the story's rocket. This was done in Rocketship X-M (1950). As noted in Hagerty's Spaceship Handbook it is not clear why the movie makers did this, because they had an elaborate model with flame and in fact cut back and forth between the model and the real V-2 launch. You can see the V2 at about 15:33 on the You-Tube copy.
https://www.youtube.com/watch?v=0KboA6IxmPo
https://www.youtube.com/watch?v=0KboA6IxmPo