What serves as the U.S. Army's tactical network backbone?

The U.S. Army's tactical network backbone is known as the Army Tactical Network (ATN). This network provides essential communication and information-sharing capabilities to soldiers in the field, enabling them to operate effectively in diverse environments and conditions. ATN integrates different types of systems and technologies to create a cohesive platform for mission command, situational awareness, and interoperability among various units.

ATN plays a crucial role in modernizing the Army's communication infrastructure, allowing for real-time data exchange, enhancing command and control capabilities, and supporting various mission requirements. By serving as the fundamental framework upon which other tactical systems rely, the Army Tactical Network ensures that units can communicate seamlessly and efficiently across various platforms and applications.

The other choices, while related to military communications or operations, do not represent the primary tactical network backbone. For instance, MCN-AE pertains to specific applications, NEC involves network enterprise capabilities, and Trojan is associated with cybersecurity aspects rather than serving as the core network backbone.