Who are the "big three", as deduced in the radio broadcast?

The "big three" are the United States, the United Kingdom, and the Soviet Union.

This list is based upn fact.

The "big three" in the novel are not revealed.

"Big Three!" Randy said. "Who's the Big Three?" "Sh-h!" said the Admiral. "Maybe we'll find out."

". . . but as yet the Big Three have been unable to reopen communications with Dmitri Torgatz. According to Radio Tokyo, Torgatz headed the Soviet government while the Soviet Union's capital was in Ulan Bator in Outer Mongolia. The medium-wave station operation from Ulan Bator is no longer heard."

"That doesn't sound like Soviet propaganda to me," Randy said. "Who is Dmitri Torgatz?"