In 1912, Trenchard learned to fly and joined the Royal Flying Corps. He became the second most important man at the Central Flying School in England and had several important jobs in the Royal Flying Corps during World War I. Trenchard was the man in charge of the Royal Flying Corps in France from 1915 to 1917. In 1918, he was the first man in charge of the Royal Air Force for a short time. He then went back to France to take over the Royal Air Force bombing attacks on Germany. Winston Churchill put him back in charge of the Royal Air Force in 1919. Over the next 10 years, Trenchard started Air Force training bases and made sure that it was used to enforce the law in parts of the British Empire. In the 1930s Trenchard was in charge of the London's police force (the Metropolitan Police) and as an older man he argued for keeping a big RAF. In modern times, some people say that Trenchard was one of the first people to argue for strategic bombing.