CSC-STD-004-85 Technical Rational Behind CSC-STD-003-85: Computer Security Requirements — Guidance for Applying the DoD TCSEC in Specific Environments, 25 June 1985. (Yellow Book)
You can download it from the following link: https://packetstormsecurity.com/files/download/13990/CSC-STD-004-85.txt
Source: https://packetstormsecurity.com/files/13990/CSC-STD-004-85.txt.html