A U.S. Army manual on psychological operations (pdf) elaborates upon the role of PSYOP in military activities.
“The employment of any element of national power, particularly the military element, has always had a psychological dimension. Foreign perceptions of U.S. military capabilities are fundamental to strategic deterrence. The effectiveness of deterrence hinges on U.S. ability to influence the perceptions of others.”
“The purpose of PSYOP is to induce or reinforce foreign attitudes and behavior favorable to U.S. national objectives… When properly employed, PSYOP can save lives of friendly and adversary forces by reducing the adversaries’ will to fight. By lowering adversary morale and reducing their efficiency, PSYOP can also discourage aggressive actions and create dissidence and disaffection within their ranks, ultimately inducing surrender.”
The 179 page manual has not been approved for public release, but a copy was obtained by Secrecy News.
See “Psychological Operations,” Field Manual FM 3-05.30, April 2005.