The starting point for this report is the Center's coding system, which classifies businesses according to industry. Many defense contractors, such as General Electric and Boeing, do not derive the majority of their profits from defense work. Therefore these contractors' PAC contributions are counted as defense-related only when they go to members of the defense and appropriations committees. The Center confirmed prime contractors for specific weapons systems with the Department of Defense. Information on subcontractors came from a variety of sources, including the contractors themselves, media reports, and organizations that monitor defense spending.
Subcontractors are sometimes difficult to identify.
The Defense Department does not maintain an easily available, centralized list of information on all defense subcontractors, weapons system by weapons system. Instead, subcontractor information is provided in the aggregate, as are top contractors. While defense contractors are often eager to communicate who their subcontractors are to members of Congress, particularly if those subcontractors are located in a lawmaker's district, they are often reluctant to release comprehensive lists of subcontractors to the general public. As a result, the information available on subcontractors for different weapons systems is sketchy. A comprehensive list for one state may be available, while a list for another is not.