If you're a US citizen with an invention, and the US government wants to take your invention for their own exclusive purposes, they are explicitly allowed to do so. Even though the patent is still yours, you cannot reveal any details surrounding it due to the secrecy order, which means that you effectively cannot actually implement or build the invention described within the patent, because if anyone other than you were to somehow possess or observe it, you would be in violation of the patent secrecy order. The one exception to this is if you assist in building the invention for a person or entity explicitly authorized by the US government. Essentially, if you want to profit from an invention in such a situation, you would have to be hired by the US government.