I am looking for the name of a movie that was on HBO in the early to mid 80's. The movie is about a group of people who volunteer to go into a bomb/nuclear shelter for a set period of time. While they are in the shelter, a nuclear war breaks out, so they think. The government staged a mock war to get the reaction of the people inside. I remember very little of it as I was very young when I saw it. Any help would be much appreciated. Thanks