At the Edgewood Arsenal in Maryland, Army doctors tested a wide variety of psychochemicals on unsuspecting soldiers. Two of those substances were the hallucinogen LSD and the mood-altering BZ. While the CIA has been interested in LSD as a 'spook drug' or truth serum, the Army saw it as a means for disorienting and confusing the enemy. It could be delivered through their water supply (which was tried) or through aerosol sprays (which didn't work very well since it dissipated very quickly.) They found BZ interesting because they felt it could increase human aggressiveness; when tested on rats, it set them to fighting savagely against each other. It might, they thought, cause the enemy to get paranoid and turn against its own forces. Other psychochemicals were tested in the hope that they might cause enemy pacification reactions (reducing the will to fight or resist), increase allied performance (by stimulating adrenalin and alertness, etc.), or outright delusions (for distraction purposes.) Many of the drugs that leaked into the hands of the counterculture were being tested by the military and the intelligence community long before, as early as the early 1950s. Drugs have always been an instrument of conquest; opium was the principal means that Britain extended its imperial ambitions into China and kept the populace from resisting.
But psychochemicals were by no means the only means of behavioral warfare being explored by the military. Fascinated by the behaviorist idea of conditioning, the military tried to explore the 'programming' of the human brain, and examined ways in which - through deprivation, sensory isolation, or punishment-and-reward - it might be made a "blank slate" for receiving new programs. The military was fascinated by the possibility of developing a Manchurian Candidate - an assassin from the enemy who could be 'brainwashed' into killing its enemies. To that end, the Army also explored hypnosis, the effect of ELF waves on human brain frequencies, and the use of sounds as signals to 'trigger' specific behavioral responses. Other low-tech methods of exercising power, such as entrapment, intimidation, and coercion, continue to be explored. There was also a great deal of research into "psychoacoustic" technology, involving the use of induced audial hallucinations and disorientation created by infrasonics or microwave technology. Such "directed-energy" weapons may well be battlefield-tested someday for behavioral warfare ops.
Other forms of non-behavioral psychological warfare revolve around what might be called 'disinformation' or propaganda. An important part of fighting an enemy is feeding them false knowledge and misdirecting them with false facts. But even in peacetime propaganda can serve to demoralize, destabilize, and divide internally a hostile enemy. Various techniques have been explored - the use of false rumours, doctored photographs and images, and "planted" news stories - fall into this category. The U.S. military in Nicaragua was accused of distributing a handbook which described vividly the arts of industrial sabotage. In Panama, they used rock music to drive Noriega out of a church where he had taken refuge, which may be the ultimate form of psychological warfare.