this period, Jews were approximately 3.3 percent of the total U.S. population but they constituted about 4.23 percent of the U.S. armed forces. About 60 percent of all Jewish physicians in the United States who were under 45 years of age were in service as military physicians and medics. Many Jewish physicists, including J. Robert Oppenheimer, were involved in the Manhattan Project, the secret World War II effort to develop the atomic bomb. Many of these physicists were refugees from Nazi Germany or they were refugees from antisemitic persecution which was also occurring elsewhere in Europe. American folk music Jews have been involved in the American folk music scene since the late 19th century; these tended to be refugees from Central and Eastern Europe, and significantly more economically disadvantaged than their established Western European Sephardic coreligionists. Historians see it as a legacy of the secular Yiddish theater, cantorial traditions and a desire to assimilate. By the 1940s Jews had become established in the American folk music scene. Examples of the major impact Jews have had in the American folk music arena include, but are not limited to: Moe Asch the first to record and release much of the music of Woody Guthrie, including "This Land is Your Land" (see The Asch Recordings) in response to Irving Berlin's "God Bless America", and Guthrie wrote Jewish songs. Guthrie married a Jew and their son Arlo became influential in his own right. Asch's one-man corporation Folkways Records also released much of the music of Leadbelly and Pete Seeger from the '40s and '50s. Asch's large music catalog was voluntarily donated to the Smithsonian. Jews have also thrived in Jazz music and contributed to its popularization. Three of the four creators of the Newport Folk Festival, Wein, Bikel and Grossman (Seeger is not) were Jewish. Albert Grossman put together Peter, Paul and Mary, of which Yarrow is Jewish. Oscar Brand, from a Canadian Jewish family, has the longest running radio program "Oscar Brand's Folksong Festival" which has been on air consecutively since 1945 from New York City. And is the first American broadcast where the host himself will answer any personal correspondence. The influential group The Weavers, successor to the Almanac Singers, led by Pete Seeger, had a Jewish manager, and two of the four members of the group were Jewish (Gilbert and Hellerman). The B-side of "Good Night Irene" had the Hebrew folk