This is an example of a standard issue AN-6540-2S flying helmet for the United States military during World War II and the immediate post war period.
This helmet was worn by Lt. Col. Marion Carl. He graduated as a member of the first test pilot class at Patuxent River Naval Air Station in 1945. He conducted pioneering jet operations from aircraft carriers; commanded VMF-122, the first Marine Corps squadron equipped with jets; and was an early Marine helicopter test pilot. He wore this helmet suit during his career as a test pilot, including his world speed record flight with the Douglas D-558-1.
This object is not on display at the National Air and Space Museum. It is either on loan or in storage.