When war enveloped Europe in 1939 the nuclear physics group of the Department recognized the serious crisis that faced Western civilization. At top of their concerns as citizens lay concerns imposed by their knowledge of what was transpiring with uranium fission. They were themselves active in obtaining data that went primarily to Fermi for his far-ranging calculations. Roberts published a paper sketching the possibilities of fission as a source of power, and back-of-the-envelope calculations of bomb designs dominated many informal discussions. The sudden and unexpected defeat of France, followed by the Battle of Britain in the summer of 1940, brought all of these concerns to a rapid focus. The group, Tuve, Hafstad, Roberts and Heydenburg, sought a research goal with direct application to preparing the nation for the struggle they were sure was coming.

There was little interest in the atomic bomb project that was coming into existence, although they cooperated in making the measurements wanted by others. They estimated that years would be required for its achievement, not to mention an enormous industrial commitment that might prove to be a misdirection of effort. Tuve's connections with the Navy, established during the ionosphere work, soon had him in consultation with ordnance officers, who were quite receptive to his offer of research talent.

The Navy's great concern was the vulnerability of ships to air attack. In the spectacular and public demonstrations after World War I by General Mitchell it had been established that an airplane could sink a battleship.