Question: The Bell X-1 was an aircraft piloted at a supersonic level by the test pilot who served in what branch of the armed forces?

Context paragraphs:
Armstrong Flight Research Center: The NASA Neil A. Armstrong Flight Research Center (AFRC) is an aeronautical research center operated by NASA.  Its primary campus is located inside Edwards Air Force Base and is considered NASA’s premier site for aeronautical research.  AFRC operates some of the most advanced aircraft in the world and is known for many aviation firsts, including critical support for the first manned airplane to exceed the speed of sound in level flight with the Bell X-1, highest speed ever recorded by a manned, powered aircraft (North American X-15), the first pure digital fly-by-wire aircraft (F-8 DFBW), and many others.  AFRC also operates a second site in Palmdale, Ca.  known as Building 703, once the former Rockwell International/North American Aircraft production facility, at Air Force Plant 42.  There, AFRC houses and operates several of NASA's Science Mission Directorate aircraft including SOFIA (Stratospheric Observatory For Infrared Astronomy), a DC-8 Flying Laboratory, a Gulfstream C-20A UAVSAR and ER-2 High Altitude Platform.  David McBride is currently the center's director.

Chalmers Goodlin: Chalmers Hubert Goodlin (January 2, 1923 – October 20, 2005) was the second test pilot of the Bell X-1 supersonic rocket plane, and the first to operate the craft in powered flight (the others having been glide tests).  He was the pilot of the project's second plane, and nearly broke the sound barrier.

Aircraft Research and Development Unit RAAF: The Royal Australian Air Force's Aircraft Research and Development Unit (ARDU) plans, conducts and analyses the results of ground and flight tests of existing and new Air Force aircraft.  ARDU consists of four flights located at RAAF Bases Edinburgh, Amberley, Richmond and Williamtown, staffed by qualified test pilots, flight test engineers and flight test system specialists.  Up until 2016 the Squadron also conducted flight test for the Australian Army with Army personnel also working within the unit.  The flight test crew are long course trained at test pilot schools including the United States Air Force Test Pilot School, the United States Naval Test Pilot School, the Empire Test Pilots' School, the École du personnel navigant d'essais et de réception and the National Test Pilot School.

Jack Ridley (pilot): Colonel Jackie Lynwood "Jack" Ridley (June 16, 1915 – March 12, 1957) was an aeronautical engineer, USAF test pilot and chief of the U.S. Air Force's Flight Test Engineering Laboratory.  He helped develop and test many Cold War era military aircraft but is best known for his work on the Bell X-1, the first aircraft to achieve supersonic flight.  He was highly respected among fellow test pilots, most notably Chuck Yeager, for his engineering skills.

Bell X-1: The Bell X-1 was a rocket engine-powered aircraft, designated originally as the XS-1, and was a joint National Advisory Committee for Aeronautics-U.S. Army Air Forces-U.S. Air Force supersonic research project built by Bell Aircraft.  Conceived during 1944 and designed and built in 1945, it achieved a speed of nearly 1000 mph in 1948.  A derivative of this same design, the Bell X-1A, having greater fuel capacity and hence longer rocket burning time, exceeded 1600 mph in 1954.  The X-1, piloted by Chuck Yeager, was the first manned airplane to exceed the speed of sound in level flight and was the first of the X-planes, a series of American experimental rocket planes (and non-rocket planes) designated for testing of new technologies and often kept secret.

Desmond 'Dizzy' de Villiers: Desmond ‘Dizzy' de Villiers AFC (7 November 1922 – 19 June 1976) was chief test pilot at de Havilland, the world’s first open cockpit pilot to reach supersonic speed (albeit inadvertently, the cockpit canopy flew off mid-flight), the second British pilot to exceed mach 2, chief experimental test pilot on the English Electric Lightning programme (making more than 1,000 flights) and who, during his test career, flew more than 6,000 hours in 130 different aircraft.

John H. Griffith: John H. Griffith was a test pilot for the National Advisory Committee for Aeronautics, one of the pilots of the Bell X-1.

Bell Aircraft: The Bell Aircraft Corporation was an aircraft manufacturer of the United States, a builder of several types of fighter aircraft for World War II but most famous for the Bell X-1, the first supersonic aircraft, and for the development and production of many important civilian and military helicopters. Bell also developed the Reaction Control System for the Mercury Spacecraft, North American X-15, and Bell Rocket Belt.  The company was purchased in 1960 by Textron, and lives on today as Bell Helicopter.

Arthur W. Murray: Arthur Warren "Kit" Murray (December 26, 1918 – July 25, 2011) was a United States test pilot.  He flew test flights on the Bell X-1 and the Bell X-5 aircraft.

Chuck Yeager: Charles Elwood "Chuck" Yeager ( ; born February 13 , 1923) is a former United States Air Force general officer and record-setting test pilot.  In 1947, he became the first pilot confirmed to have exceeded the speed of sound in level flight.

Supporting paragraphs: Bell X-1 Chuck Yeager
Answer: United States Air Force