Chapter 12 of the current best seller, "You Are Now Less Dumb," describes a 1954 psychology experiment that makes Lord of the Flies look like a documentary. A psychologist took two busloads of boys out to a park, and left them to their own devices. Over a span of several days, the scientists had to intervene repeatedly to stop the groups from killing each other, eventually terminating the experiment early because of this.

Although the citation for that chapter is a 1961 book by the chief psychologist, I am sure that it must've been reported much earlier. The timing leaves open the barest possibility that Heinlein heard of it in advance. When I read it, it instantly reminded me of Tunnel.

Here's a reference I googled from which you can get search terms to possibly find a contemporaneous publication: http://www.age-of-the-sage.org/psycholo ... iment.html.

Psychologist Muzafer Sherif and his wife Carolyn conducted the Robbers Cave Experiment in late June of 1954; apparently it was the third in a series of experiments (earlier studies in 1949 and 1953) that placed arbitrary groups of kids in conflict with each other. The first publication was a research report that he sent to colleagues in Aug 1954, and it was more formally documented in American Sociological Review, Dec 1954.

The 1949 study was documented in Social Psychology at the Crossroads (J. Rohrer and M. Sherif, edits., New York: Harper, 1951), Chapter 17, and more fully in M. Sherif and C. W. Sherif, Groups in Harmony and Tension (New York: Harper, 1953), chaps 9 and 10. The 1953 study was documented in M. Sherif, B. J. White, and O. J. Harvey in “Status in experimentally produced groups”. American Journal of Sociology, 1955, 60, 370-379.

Dallas Morning News Dec 15, 1951: “To illustrate his point, [Muzafer Sherif] cited a test in which normal, healthy American boys in a summer camp were divided into two groups and given competitive assignments in work and play. The two groups became immediately hostile, fought bitterly.”

Tunnel was published in 1955 and the Opus List says it was written in Dec 1954. It is certainly possible that RAH had run across an account of Sherif’s work and it was in some way inspirational for Tunnel.