Which branch of the military is responsible for expeditionary operations, rapid response, and amphibious assault?

The Marine Corps is designated as the branch of the military responsible for expeditionary operations, rapid response, and amphibious assault. This role stems from the Corps' unique training and capabilities, making it adept at deploying quickly and engaging in operations that require both land and maritime skills. The Marines are often the first to respond in crisis situations, capable of operating in diverse environments and conducting operations from the sea, which emphasizes their amphibious capabilities.

The structured training that Marines undergo includes specialized skills in maneuver warfare and ground combat, and they are organized into Marine Expeditionary Units (MEUs) that can be deployed swiftly on short notice. This allows for flexibility and responsiveness that is critical for handling unforeseen circumstances in various theaters of war. In addition, the Marine Corps has the unique ability to conduct joint operations alongside the Navy, as they both share operational goals when executing amphibious assaults and other missions involving maritime environments.

The other branches of the military, while they may have capabilities for rapid response or joint operations, do not specifically focus on the amphibious assault aspect or maintain the specialized expeditionary forces that the Marine Corps does.