There are many pathways for a start-up or established company to sell a new technology to the DoD. Bidding on contracts, selling direct and applying for grants are just a sample of the methods available to sell or receive funding from the US government. However, one step is often overlooked and that is actively marketing or "teaching" potential DoD customers about your product or service.
The US government has no shortage of problems they're trying to solve. However, I often speak with small businesses that are discouraged when searching for opportunities to do business with the DoD or other federal agencies. They are just un-able to find a published need or request for their specific solution (common if you've developed a technology that could fundamentally change the way an existing system works or mission is conducted).
The key for a company with a new or disruptive technology, is to get in front of potential customers and brief (or better yet demonstrate) their solution. Government acquisition professionals are often looking for innovative ways to solve problems, in fact, there are specific shops set up specifically for this! The key is getting your solution in front of the right program managers, engineers and decision makers so they know an alternative solution to an existing problem set is available.
Let's say DOD office X has a data collection problem their trying to solve, If this was traditionally solved by a reconnaissance aircraft, they may be looking for an expensive aircraft sensor to be built, eventually resulting in a Request for Proposal (RFP) for an airborne sensor. However, start-up company Y has created a ground based software tool that can collect the same information (at a fraction of the cost as the airborne sensor). There are two ways this could go depending on Company Y's actions:
Company Y carefully monitors online sites to see if an applicable RFP is issued. After a year they give up, as the RFP they are waiting on never appears or their proposal gets beat out by a large defense contractor.
Company Y, due to a robust marketing and business development campaign, gets in front of the right acquisition team to present their solution, learns of an opportunity months before an RFP goes out, and eventually goes on contract.
Although this example is a hypothetical, it happens time and time again. Companies that consistently win contracts with the federal government become experts at cultivating relationships with the right government decision makers. This becomes even more important if you have developed a capability that is new and unknown to the DoD!