Nightwatch communications are on the USAF ZULU channels. I have listed all the ZULU channels and their frequencies (KHz) that I can find. 
The National Emergency Airborne Command Post (NEACP/Nightwatch) missions were set up in 1962 as a method of providing a secure command and control platform for the National Command Authority during a nuclear crisis. You'll hear the Airborne Command Post aircraft "Looking Glass" on these frequencies passing messages to USAF and USNAVY nuclear assets such as bombers, missile, and balistic missile submarines.
Special thanks to G.Fetter for the reference for this info.