In his essay "How to Start a Startup" (http://www.paulgraham.com/start.html), Paul Graham asserts:
"Avoid starting a startup to sell things to the biggest company of all, the government. Yes, there are lots of opportunities to sell them technology. But let someone else start those startups."
The U.S. government has paperwork hoops to jump which takes time. I believe you need to get on the GSA schedule in order for departments to be able to purchase your products or services. Many things are competitively bid.
On the plus side, the government may be a source of funding. Look into the Office of Naval Research or grants.gov to see what they are looking to fund.
