Here are a number of sites, resources that as an enthusiast, WW historian, serviceman or family member of the 20th Air Force you might enjoy and find relevant.
Army Air Corps Library and Museum World War II History Museum. Army Air Corps. Army Air Forces.
20th Air Force History 20th Air Forces Formation, Dates, Commanders, Theaters, Order of Battle.
US National Archives
Air Force Historical Research Agency
Sons of Liberty Museum US Army, US Marines, US Navy, US Air Force. World War I, World War II, Korea, Vietnam History. Military History. Museum.