slowly during the summer monsoon. Overuse of the small number of aircraft available, spotty maintenance, and a lack of spare parts led to numerous groundings until overhauls could be effected. In particular the lack of replacement tires and spare engines held down operations even after eight of the C-47s sent to the Middle East returned in August. For a short period of time engines intended for P-43 fighters of the Chinese Air Force were adapted for use on C-47s but the supply of those proved small. Although three bases constructed by the British on tea plantations at Chabua, Mohanbari, and Sookerating were declared operational in August 1942, and construction of a fourth began at Jorhat, none were expected to be ready for all-weather operations before November or December because of problems with unskilled indigenous labor and the failure of promised heavy equipment to arrive from the United States. Throughout the monsoon rains Dinjan remained the chief transport base. The dismal results of the India-China Ferry to this point led to a proposal in Washington to turn over control of the operation entirely to CNAC, which would place U.S. military personnel in a combat area under foreign civilian control. Stilwell vigorously and successfully opposed the plan. He reinforced his position by insisting that CNAC lease its C-53s and crews participating in the airlift to the USAAF to assure that they would carry only essential cargo and not commercial activity. The airlift lost its first aircraft to accident on 23 September 1942, presumably from icing, after which losses of transports increased sharply. Protection of the aerial supply line became the primary mission of the Tenth Air Force. When the summer monsoon ended, the Japanese were expected to try to sever the last remaining connection to China, and although 10AF's CATF was adequate for the defense of the eastern end, little had been done to create an antiaircraft defense around the four Assam airfields. The 51st Fighter Group was nominally responsible for fighter protection, but two of its three squadrons had been stripped of their aircraft and personnel in July to equip the group's third squadron and round out the newly activated 23rd Fighter Group, both in China with the CATF. The 51st FG remained in Karachi awaiting aircraft and personnel. Requests for more antiaircraft guns, a weather squadron, and radios and landline communications equipment for an early warning system were immediately approved