After watching this[0], please feel free to make a donation to any FOSS organization of your choosing such as the Open Source Initiative[1]. You can learn more at the DARPA Open Government website[2].
...the FOSS enthusiast would have to be naive to think DARPA wasn't aware of FOSS and had FOSS efforts. But more importantly -
People in defense track everything - down to the wafer. Going "have you tried FOSS, you could verify everything!" To someone in an industry where we...already verify everything...would be hilarious.
A naive FOSS enthusiast would probably make their ideas available freely and openly. There's nothing preventing you from getting your wish as well, though.
[0] https://www.youtube.com/watch?v=7UF56umERjs&list=PL6wMum5UsY...
[1] https://opensource.org/
[2] https://open.defense.gov/Initiatives/DARPA-Open-Catalog/