Was it the inspiration for The X-Files?
If you watch the series and know it's characters, then it's for you:
American government conspiracies against its own people apart, this movie has certain religious imagery and insinuations and nuances which many of the X-Files character relate to or undergo in reference to their past life experiences and incidents. Moreover, the Vietnam veterans' experience or the syndromes they face which is the dominant theme of this film, has been explored in many of the X-Files episodes such as Sleepless(s02e04) and Unrequited(s04e16) (There might be many more, I don't remember now). Skinner was a veteran and he recounts his near-death experience to Mulder in one episode. And all X-Files fans (I'm a die-hard one myself) sure know that Scully has her numerous trysts with the religious when confronted and crippled by the scientific.
Don't get me wrong; I'm not saying that one ripped the other off. I'm an avid lover and admirer of this movie as well as the series. My affair with X-Files is old and I just now came across this movie and was struck by its ingenuity, brilliance and atmospheric quality. I am aware that Chris Carter has cited the series Kolchak as his series' primary influence; I'm just suggesting that this movie might be another one among a few.
Your thoughts guys..