A link to the Ars Technica article Best bad idea ever? Why Putin’s nuclear-powered missile is possible… and awful was included as a comment below my question How did Northrop Grumman propose to make the Global Hawk nuclear powered?.
That article links to the video Nuclear Ramjet (Project Pluto) to Drive "Big Stick" SLAM Missile circa 1959 USAF-Convair.
The narrator sounds to me to possibly be the actor Peter Graves, and there are comments about this on the video's page as well.
Did Graves work extensively as a narrator for the US government in defense related films in the 1950s and 1960s?
edit: This answer links to the video Gyroscopic Instruments - U.S. Navy Aviation Training Film (1960) which of course does not have credits either, but that certainly sounds like Peter Graves to me.