I know nothing about the Hays plant, but there were a large number of defense plants built from the ground up all over the USA during 1940-41 as it was becoming evident that the US was quickly being drawn into the European and Far East conflicts. In fact, the end of the Great Depression was brought about largely because of these immense defense plant construction projects. As a general rule, these defense plants were owned by the U. S. Government and operated by various civilian contractors (and sometimes multiple contractors for different areas of the same plants). There was usually a military contracting presence at each facility in order to oversee production. Many of those same WWII-built defense plants remained viable clear through the Vietnam era, but were not necessarily in operation the entire time - meaning that after use during WWII, Korea, and Vietnam respectively, the plants were placed in standby caretaker status but were not producing anything, or were operating at some reduced level, in order to keep the production equipment and facilities maintained. Many such defense plants were declared surplus in the 1980s and 1990s and the properties were essentially given to state and local government agencies (usually called Local Redevelopment Authorities, or LRAs) for redevelopment of the properties into civilian activities, such as business or industrial parks, public recreational areas, etc.
