Arnold had been selected to serve on the MPAA's Production Defense Co-ordination Committee. That same year he was selected to sit on the board of the MPAA's Oscar committee for technical awards. 1940 also saw Arnold invent a new camera boom and dolly, considered a radical improvement at the time. The boom allowed the camera to film from ground level all the way to 16 feet. In 1941, while he remained on their Board of Governors, he was replaced as president by Fred Jackman. Arnold stepped down due to his increasing duties at MGM. In 1941 he was appointed to a committee to discuss and standardize the use of 16mm equipment in the film industry. The committee was set up by the Research Council of the Academy of Motion Picture Arts and Sciences (AMPAS). In 1942 Arnold was again a member of an AMPAS committee, this one recommended changing the film speed from 24 to 18 frames per second. This would result in saving 35,000,000 feet of film each year. That same year, Arnold was selected to be the sole cinematography representative on the industry's War Activities Committee. In 1942 Arnold was one of a handful of cinematographers selected to train servicemen in the Signal Corps on how to take combat footage. By the end of 1943 he had trained over 350 men in the service. In 1946, to help out fellow out cameraman (now working for him at MGM) Paul Vogel, who was working on the film Lady in the Lake, Arnold developed a special camera dolly which had four independent wheels. The film was shot from the POV of the protagonist, and the independent wheels allowed the camera to "walk" through doorways and upstairs, simulating natural movement. Arnold invented the Ro Boom, used by MGM in the 1940s. In 1948 he invented a new controller and motor for the boom. The new device allowed a single operator to move the boom at greater speeds. It had graduated speeds forwards and backwards, as well as dynamic braking through the motor. For the 1949 film Neptune's Daughter, Arnold oversaw the development of a combination camera elevator and crane, which allowed vertical travel shots, mid-air shots, and use of the camera anywhere from floor to ceiling without the need for extra equipment. Arnold made another improvement to his Ro Crane in 1952, which allowed technicolor cameras to utilize the crane. He