war, tying down more than a million Japanese troops who might otherwise threaten the Allied strategic offensive in the Pacific. The Japanese invasion of French Indochina closed all sea and rail access routes for supplying China with materiel except through Turkestan in the Soviet Union. That access ended following the signing of the Soviet–Japanese Neutrality Pact in April 1941, and the Burma Road became the only land route. The rapid success of Japanese military operations in Southeast Asia threatened this lifeline, prompting discussion of an air cargo service route from India as early as January 1942. Chiang's foreign minister, T. V. Soong, estimated that 12,000 tons of materiel could be delivered monthly by air from India if 100 C-47 Skytrain-type transports were committed to an airlift. Chinese Air Force Major General Mao Bangchu was tasked with leading the exploration of suitable air-routes over the dangerous Himalayas in 1941, and CNAC pilot Xia Pu recorded the first flight from Dinjan, India, to Kunming, China, during November of that year in what was to become the route now known as "the Hump". On 25 February 1942, President Roosevelt wrote General George C. Marshall that "it is of the utmost urgency that the pathway to China be kept open", and committed ten C-53 Skytrooper transports for lend-lease delivery to CNAC to build its capability to 25 aircraft. When the newly created Tenth Air Force opened its headquarters in New Delhi under the command of Maj. Gen. Lewis H. Brereton in March 1942, it was assigned the responsibility of developing an "India-China Ferry" using both U.S. and Chinese aircraft. Although he was never given command authority over aircraft or personnel, the officer responsible for the India-China Ferry was Brereton's chief of staff Brig. Gen. Earl L. Naiden, who held that responsibility until mid-August. From its onset, the air route was predicated on operating two branches, unofficially deemed "commands": a "Trans-India Command" from India's western ports to Calcutta, where cargo would be transshipped by rail to Assam; and the "Assam-Burma-China Command", a route from bases in Assam to southern China. The original scheme envisioned the Allies holding northern Burma and using Myitkyina as an offloading terminal to send supplies by barge downriver to Bhamo and transfer to the Burma Road. However, on 8 May 1942 the Japanese seized Myitkyina and this, coupled with the loss of Rangoon, effectively cut Allied access to the Burma Road.