Hospital corpsmen lift a simulated casualty into M997 ambulance during a casualty evacuation drill at Marine Corps Air Station Futenma, Okinawa, Japan Dec. 8, 2015. The casevac course is two weeks long and gives the students a better understanding of what it means to be a corpsman. The corpsmen are with various units with III Marine Expeditionary Force. - Hospital corpsmen lift a simulated casualty into M997 ambulance during a casualty evacuation drill at Marine Corps Air Station Futenma, Okinawa, Japan Dec. 8, 2015. The casevac course is two weeks long and gives the students a better understanding of what it means to be a corpsman. The corpsmen are with various units with III Marine Expeditionary Force.