Following the Japanese attack on Pearl Harbor in December 1941, the United States declared war on Japan, and President Roosevelt sought an immediate counterattack for the humiliation of Pearl Harbor; in the urgency to keep China resupplied for the new Sino-US joint effort in the war against Japan, General Joseph Stilwell was sent to Generalissimo Chiang Kai-shek on a top secret arrangement for transferring of North American B-25 Mitchell bomber support equipment, radio-homing navigational aids and 100-octane avgas into China to support the planning of what was to become the Doolittle Raid against the Japanese home islands. The badly needed high-octane avgas and new equipment in China for the renewed war effort against the Empire of Japan were now increasingly being freighted via the risky Himalayan air-route known as "The Hump". As Japan's focus have shifted towards the Pacific campaign, and much of the Japanese aerial-combat assets and experienced personnel had been diverted to support the war in the Pacific, the offensive campaign against Chonqing and Chengdu have been much curtailed, nonetheless, modern interceptor aircraft possessing far greater speed and firepower, supported by ground-based radar equipment, and new aircrew training supported by the US and allied partners allowed the Chinese Air Force to be in a much better position to fight back by August 1943. The last recorded air raid of the campaign took place on 19 December 1944.