When World War I broke out Ravel felt very strongly that he wanted to do something for his country. However, he was not allowed to join the French army because he was 2 kg underweight. So he became a driver for the motor transport corps. In 1916 he became ill with dysentery. After a time in hospital he was taken back to Paris to get better, but then his mother died and this had a terrible effect on him. The war years had slowed him down as a composer. He had composed "Le Tombeau de Couperin" (well-known both as a piano solo piece and for orchestra) which looks back to the style of music in the Baroque period. It took him a long time to finish "La Valse" ("The Waltz"), one of his most popular pieces.