As outlined in the General Structure of the U.S. military, the primary branches focus on building and training forces, while [[Combat Command]] focus on deploying them to theaters of operations around the world. In addition, the DoD boasts a number of DoD-specific or cross-branch functional sites.
Here are the primary web sites for your reference.
As the service branches focus on recruitment and retention, they will have both a public-face recruiting website, as well as an informational website. Sometimes, they even have primary news magazines.