Who provides oversight to ensure military communications remain secure?

The Central Security Service (CSS) is responsible for overseeing and ensuring that military communications remain secure. This organization plays a critical role in safeguarding communications within and between military branches by developing, implementing, and enforcing security measures designed to prevent unauthorized access and to protect classified information. The CSS works alongside other agencies to enhance security protocols and provide training and resources necessary for secure communications.

While other organizations listed have important roles within the Department of Defense, they do not focus specifically on the oversight of military communications security. The Defense Intelligence Agency primarily deals with intelligence gathering and analysis, while the Defense Contract Management Agency oversees defense contracts and related financial aspects. The Defense Threat Reduction Agency focuses on reducing threats from weapons of mass destruction, rather than managing the security of military communications directly. This specialized focus of the Central Security Service on securing military communications distinguishes it as the correct answer.