When World War I broke out in 1914, Curie devoted her time and resources to helping the cause. She championed the use of portable X-ray machines in the field, and these medical vehicles earned the nickname "Little Curies." After the war, Curie used her celebrity to advance her research. She traveled to the United States twice— in 1921 and in 1929— to raise funds to buy radium and to establish a radium research institute in Warsaw.