EAMs are frequently read on the HF-GCS frequencies and usually won’t take you long to hear one. They begin with a 6 letter header, this preamble could have a few different uses, but NPS states for Minuteman Missile launches “The preamble told the crew which edition and page number of a non sealed authenticator to use. Once at the right page the crew would know what message checklist to use.” The receiving crew has access to an emergency action checklist binder where the message and instructions are copied to. Then the message continues afterward and is repeated.