It was used again by the Army in the mobilization of 1940 that preceded the American entry into World War II. As part of the nationwide internment of Japanese Americans approximately 1,000 Japanese Americans were kept there, under tight security, behind multiple layers of barbed wire fence. Camp Upton was also used to hold Japanese citizens who were in New York City at the time war broke out, including businessmen with whom the governments of Japan and the United States negotiated an exchange. Camp Upton later housed a convalescent and rehabilitation hospital. In 1946, after the camp was closed, the federal government chose the site to build a nuclear research facility that would retain America's preeminence in that field. The former Camp Upton was renamed Brookhaven National Laboratory and was operated by AUI, a consortium of universities, for the United States Atomic Energy Commission. Irving Berlin, while stationed at Camp Upton, wrote a musical, "Yip, Yip, Yaphank", which included the memorable song "Oh! How I Hate to Get Up in the Morning." The musical was turned into a 1943 movie "This Is The Army" which starred Ronald Reagan.