Which branch of service employs its attack rotary wing aviation primarily as a CAS platform?

The Marine Corps primarily employs its attack rotary wing aviation as a Close Air Support (CAS) platform due to its unique operational requirements and integration with ground forces. The Marine Corps focuses on supporting ground troops during combat operations, and their helicopters, such as the AH-1Z Viper, are designed to deliver direct fire support in close proximity to friendly forces. This capability allows for quick reactions to dynamic battlefield conditions, providing essential support to Marines engaged in ground operations.

Additionally, the Marine Corps emphasizes the combined arms approach, integrating air and ground forces to enhance overall combat effectiveness. The training and doctrine of the Marine Corps reflect this goal, placing a strong emphasis on the use of rotary wing aviation to provide close air support that is responsive and tailored to the needs of the infantry and other ground forces. This mission alignment is what differentiates the Marine Corps' use of attack helicopters from the other branches, where their roles and operational focuses may vary.