One fascinating aspect of this decade was the proliferation of new military types. Within the space of three years, 1934 to 1936, there occurred the debut of the Messerschmitt Bf 109, Hawker Hurricane, Supermarine Spitfire, Boeing B-17, Heinkel He 111, Curtiss P-36, Mitsubishi G3M, Morane-Saulnier MS.406, and many others that would see action in World War II. Quite remarkably, given the disparity in the resources of each country involved, these new aircraft had comparable performance parameters, which speaks to the genius of their designers.
In the years after World War I, philosophies of airpower appeared. Some were authored by well-known leaders such as the RAF's Hugh Trenchard, Italy's Giulio Douhet, and the United States' Brigadier General Billy Mitchell. Although there were many differences in their respective approaches, all agreed that command of the air was essential: The way to win a war was to attack the "vital centers" of the enemy--before they attacked yours. While their ideas were sound, they were not backed financially by any of the democratic nations, which allowed their armed forces to fall into complete disarray in the years between the wars. This was in sharp contrast to the totalitarian countries, including Germany, Japan, and the Soviet Union, where the military budget funded strong air forces.
Germany and Japan were thus endowed with a tremendous advantage at the beginning of World War II. By choosing to determine the date the war would start, they timed the introduction of new technology to their air forces so they could be at maximum strength when war began. Thus, for Germany on September 1, 1939, and for Japan on December 7, 1941, their respective air forces were at the peak of their form. Both had the latest and best aircraft, both had extensive combat experience (Germany's gained in Spain, Japan's in China and in border conflicts with the Soviet Union), and both would use them to overwhelm initially weaker enemies.
Air power allowed Germany to defeat Poland, Denmark, Norway, Holland, Belgium, and Luxembourg in swift campaigns that were relatively inexpensive. Air power in fact seduced Japan, allowing it to make the colossal mistake of becoming involved in a World War against China, the United States, and Great Britain. But it also allowed Japan to make a series of sweeping victories in late 1941 and for the first five months of 1942.