Jewish Americans have served in the United States armed forces dating back to before the colonial era, when Jews had served in militias of the Thirteen Colonies. Jewish military personnel have served in all branches of the armed forces and in every major armed conflict to which the United States has been involved. According to the U.S. Department of Defense, as of 2006 there were currently 3,973 known Jewish servicemen and servicewomen on active duty. A number of Jewish American servicemen have gained fame due to their military service, and many have received awards and decorations for distinguished service, valor, or heroism. More than 20 Jewish servicemen were awarded the military's highest award, the Medal of Honor. Many other American Jews who served in the military later achieved prominence in business, politics, science, entertainment and other fields. Foreign-born Jews have also been significant in the development of American military science and technology—including physicists Albert Einstein, J. Robert Oppenheimer, Richard Feynman, and Edward Teller, who were important in the Manhattan Project, which led to the development of the first nuclear weapons.