Albert Einstein Einstein did not return to Germany. He settled in the United States and became an American citizen in 1940. On the eve of World War II, he endorsed a letter to President Franklin D. Roosevelt alerting him to the potential development of "extremely powerful bombs of a new type" and recommending that the US begin similar research. This eventually led to the Manhattan Project. Einstein supported the Allies, but he generally denounced the idea of using nuclear fission as a weapon. He signed the Russell–Einstein Manifesto with British philosopher Bertrand Russell, which highlighted the danger of nuclear weapons. He was
Hans Albert Einstein recognition for more than twenty years of devoted and distinguished service to Applied Mechanics Reviews by the American Society of Mechanical Engineers (1972). In 1927 Hans Albert Einstein married Frieda Knecht. Albert disapproved of Frieda much as his parents had of Mileva. Einstein and Frieda had four children: Frieda died in 1958, and Hans Albert later married neurochemist Elizabeth Roboz (1904–1995). Einstein was an avid sailor, frequently taking colleagues and family out for excursions on the San Francisco Bay. On his many field trips and academic excursions, he took thousands of pictures, many of which he developed himself and presented