The Army Signals Communications Centre contained modern teleprinters, telex, Morse code and radio channels. Cryptographers also transcribed messages into code.

In addition to the Signals Centre, a “Shadow Exchange” was built on the site consisting of a structure with large logs and a protective bomb blast wall. The communications equipment inside was identical to that contained in the Flinders Street Post Office. If the Post Office was damaged in an air raid then the Shadow Exchange was to connect to the Southern and Western phone cables that ran nearby and perform as a communications backup.

Plans for a more permanent emergency exchange...