How did world war 2 affect the growth of modern private security?

During the World War II the industry and the manufacturing of weapons by the war production plants was a major enterprise and the need for a trained security increased exponentially. The on site security was needed to prevent theft, sabotage and espionage. The security companies even started training their own security staff which was well trained and their training in time was close of that the police got.  Some companies even had their own private investigators among their number.