If I had a DARPA idea?

What if I had an idea for DARPA?

How would I go about submitting it to them?

In writing. Contact info is available at their website.

Before sending in an unsolicited idea, maybe you should start by looking at a list of projects for which they’re soliciting solutions.

It doesn’t just have to be DARPA either, the Department of Defense has many other departments to which to apply for funding for developing a new idea. It is definitely easiest/best to apply for one of the announced solicitations (btw application does not constitute a public disclosure for patenting concerns). If you tell us more closely what field/area your idea is in (biodefense, armor, battlefield medicine, warfighter health), we may be able to direct you better to the best department.