ID this apocalyptic movie comedy (WTF?)

I’m referring to a movie, probably made in the 1950s or early 1960s where there was an imminent threat of nuclear war. I know this sounds like Dr. Strangelove, but it isn’t. I saw it on TV, probably sometime during the 1970s. All I remember is that at the end the bomb hits while the principal characters are huddled in the back of a big-rig truck, while the world–and the movie–end.

I realize this concept doesn’t make sense–a funny movie about nuclear war–but it really did work, and was funny, and enjoyable.

Does anyone remember this movie?

This Is Not A Test