Looking at the entire U.S. government, military and intelligence agencies are the most circumspect and make the smallest amount of information publicly available. This is partly due to the nature of military and intelligence activities, but it is also part of the institutional culture to tightly control information and its dissemination. In addition, service members face severe penalties for unauthorized release of information.
Military agencies and units have public affairs officers who may be the first point of contact. It is helpful to have an understanding of where the agency fits in the military hierarchy.
The Department of Defense relies heavily on contractors to do everything from building weapons systems to running computer systems to preparing meals. It can be difficult to get information about the number of government contractors working for defense agencies and the different types of work they are contracted to perform. The Center for Public Integrity is one organization that tracks defense contractors. USAspending.gov allows you to search for government contractors by state.
Outside organizations often do a better job of compiling data about defense industries and military activities. Here are some examples:
Jane's publishes analytic reports about weapons systems, defense and intelligence strategy, and budgets. However, the reports are available by subscription only. Another subscription-based resource is GlobalSecurity.org.
Think tanks like Brookings Institution and Rand Corporation produce studies of defense spending, arms control, and security issues. Harvard University offers a Think Tank Search to search hundreds of these institutions.
Finally, the Government Accountability Office, a branch of Congress, conducts thousands of studies on military programs and expenditures.