How many people were in the US Air Force at the start of World War 1?

Answer 1

None. There was no US Air Force until the end of World War 2.

That answer is quite literal. The "US Air Force" was created in 1947 as a separate branch of the military. However, the US did have fledgling aviation organization as early as 1908, but under a different name.

AnswerThe Aeronautical Division, U.S. Signal Corps(1907-1914) was the first progenitor of the United States Air Force, and as such is the first military air organization. A component of the U.S. Army Signal Corps, the Aeronautical Division did not contain any subordinate units during its existence. This began as a unit that operated lighter-than-air balloons. IN 1908 they began operating rigid-frame dirigibles. In 1909, the first Wright Brothers airplane was accepted into their inventory. The U.S. Navy purchased its first plane, a derivative of the Curtiss Golden Flyer, in July 1911.

The United States Army Air Service was established on May 24, 1918, after U.S. entry into World War I, which separated it from the Signal Corps.

Prior to WW1, the US had very few airplanes. Most were stationed in Texas for training and the pilots out numbered the aircraft. Most of the planes were out-dated by European standards. The French, Germans and Italians had developed more advanced aircraft.

In 1910, the United States had only 18 licensed pilots and 193 in 1912. But in much less populous France, there were 339 licensed pilots in 1910 and 968 in 1912. Both Germany and Great Britain had many more pilots than the United States. In 1912, the militaries in France, Germany, Russia, Great Britain, and Italy had more aircraft than the United States (France had 25 times as many). In 1913, France spent more than 60 times the aviation budget of the United States, Russia and Germany 40 times, and Great Britain 24 times as much. (Source: Ref 1)