When the U.S. Department of Defense launched its open source project in February, 2017, the intent was to use a proposed Defense Open Source Agreement (DOSA) for project contributors in an attempt to use contract law to “attach” open source licenses to individual projects. The DOSA was proposed as an alternative to using an existing open source license or creating a new one. DoD allowed a short period of time for the public to comment on the proposed agreement.
After receiving public comments on the proposed DOSA, DoD decided to move away from the proposed agreement and contract law in general and focus on the contribution process itself. Now the plan is to use widely-adopted open source licenses for projects when copyright is applicable. The intent is to not attach licenses to code written by government employees because code written by government employees within the scope of their employment is not eligible for copyright protection under U.S. law. For contributions that do qualify for copyright protection, a Developer Certificate of Origin will be used to designate a license.
The Developer Certificate of Origin asserts and provides that the code contributor is the creator of the contribution (or has the authority to distribute it) and that the contributor is making the contribution available under the specific license associated with the project.
More information can be found on the code.mil github FAQ page.