When did the army use LSD in experiments?

It was in the 1950s and 1960s, in a project called MKULTRA, in which the government tried to master mind-control (no joke!). There is much belief of a conspiracy surrounding this project. It's a very interesting topic, if you are interested, look up MKULTRA or Frank Olsen (a "suicidal" researcher for the project, who was more likely the victim of political homicide). There's tons of information on these topics.