Loosely based on Robert Heinlein's novel The Puppet Masters.
The outdoor shots of the barracks are actual WWII barracks and not a set. Don't know where they were located. Possibly Ft. MacArthur in San Pedro, CA, as they had those types of barracks up to 1975 and is relatively close to the studios.
Considered unsettling in its day due to male rape symbolism (before "male rape" was a term).
Some of the revolvers used in this episode are fitted with suppressors or as mistakenly called silencers. They do not suppress sound on a revolver.