What makes you think that? If they were none would bother filing patents, nor fight for their intellectual property rights. Believe me, they do both. In fact they fight for proprietary rights to stuff they developed on your nickle, if only they put in a penny or two of their own to prime the pump.
National defense industries are exempt from patent laws -- this is fact. They also don't publish their findings (i.e. they don't apply for patents), because doing so would also violate national security act. They're free to use any patents they want without royalties.
In other words, they're free to use commercial patents without royalty and they dont' publish their work on public patents like commercial entities. When you get a patent, you HAVE to disclose how it works, so by disclosing it, you're giving away secrets.
See my post #56.