Philippe Perrin (Colonel, French Air Force) (born January 6, 1963) is a French test pilot and former CNES and European Space Agency astronaut.
Kenneth O. "K.O." Chilstrom (born April 20, 1921) is a retired United States Air Force officer, combat veteran, test pilot, and author.
 He was the first USAF pilot to fly the XP-86 Sabre, chief of fighter test at Wright Field, commandant of the U.S. Air Force Test Pilot School, and program manager for the XF-108 Rapier.
 Chilstrom was a pilot in the first jet air race and delivered the first air mail by jet.
 He flew over eighty combat missions in the Italian Campaign of World War II and tested over twenty foreign models of German and Japanese fighters and bombers to evaluate their strengths and weaknesses.
The National Test Pilot School (NTPS) is the only civilian test pilot school in the United States, located in Mojave, California.
 It is organized as a not-for-profit educational institute under California state law and is governed by a Board of Trustees.
 NTPS is one of the seven test pilots schools worldwide recognized by the international Society of Experimental Test Pilots (SETP), giving pilot graduates of NTPS instant initial acceptance into their Society.
 The other six schools that receive this recognition are military or military-sponsored schools.
Roberto Vittori (born 15 October 1964 in Viterbo) is an Italian air force officer and an ESA astronaut.
 After graduating from the Italian Accademia Aeronautica in 1989, Vittori flew in the Italian Air Force.
 He then trained as a test pilot in the United States.
James E. Brown III (born August 15, 1954) is an aerospace executive, test pilot instructor, and former United States Air Force officer.
 , he is the chief operations officer and test pilot instructor at the National Test Pilot School located in Mojave, California.
Boone Tarleton Guyton United States Navy, (September 4, 1913 – April 4, 1996) was a Naval Aviation Cadet, experimental test pilot, author and businessman.
 In a flying career spanning the biplane era through the jet age, Guyton was perhaps best known for his test pilot years at Vought-Sikorsky (Chance Vought) and his participation in the development of the F4U Corsair and various other military aircraft including the OS2U Kingfisher and the radical Vought V-173 flying pancake.
Robert M. Stanley (August 19, 1912 – July 16, 1977) was an American test pilot and engineer.
 He became the first American to fly a jet aircraft on October 2, 1942, as a civilian test pilot for Bell Aircraft.
 He flew the Bell XP-59A Airacomet, which was the United States’ first turbojet aircraft.
 The flight took place at Muroc Dry Lake, California.
 The Airacomet is on display at the National Air and Space Museum in Washington, D.C.
Clarence Emil "Bud" Anderson (born January 13, 1922) is a retired officer in the United States Air Force and a "triple ace" in World War II.
 During the war he was the highest scoring ace in his P-51 Mustang squadron.
 This was the same squadron as well known test pilot (and first pilot to break the sound barrier) and ace Chuck Yeager, and they have remained lifelong close friends.
 Towards the end of Anderson's two combat tours in Europe in 1944 he was promoted to major at age 22, an extremely young age even for a highly effective officer in wartime.
 After the war Anderson became a well regarded fighter test pilot, and a fighter squadron and wing commander.
 He served his wing commander tour in combat in the Vietnam War.
 He retired as a full colonel in 1972, after which he worked in flight test management for McDonnell Douglas.
 A member of the National Aviation Hall of Fame, Col. Anderson has remained a sought after speaker at aviation and military events well into his 90's.
Micky Axton (January 9, 1919 – February 6, 2010) was an American aviator who was a test pilot during World War II.
 Axton was "one of the first three Women Airforce Service Pilots to be trained as a test pilot" and was the first woman to fly a B-29.
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.

Question: Who trained as a test pilot in the United States, Roberto Vittori or Philippe Perrin?
Answer: Roberto Vittori