While the Ministry had given him full security clearance, the Brigadier wouldn't tell him about the Doctor's origin and American UNIT agent Bill Filer shunned him as a security risk. Chinn was completely unaware who the Master was. (TV: The Claws of Axos) What he didn't know was that the Defence Minister loathed him and only gave him the UNIT task to get him out of the way. As the Ministry was clashing with UNIT at the time, it was hoped that either Chinn or UNIT would be destroyed by the other or, at the least, cancel each other out. (PROSE: Who Killed Kennedy) The Minister would go as far as to imply to Chinn he was "our man on the spot, in more ways than one". (TV: The Claws of Axos)