WWII: military spending as a share of national income 1939-1944
There were also notable fluctuations that coincided with major events for corresponding powers. These included the UK's mobilization of its defenses in 1940, after Germany took most of Western Europe; the spike in Soviet military spending after Operation Barbarossa in June, 1941; and the U.S. entry into the war following the Pearl Harbor attacks in December, 1941.