George C. Kenney to witness firsthand how France's defenses were insufficient. (Each of these men later attained the rank of general.) Kelsey and the group of American airmen saw that self-sealing fuel tanks were critical in air combat. As well, fighters appeared to require bullet-proof windscreens and better oxygen systems. After passing through Paris, Spaatz and Kelsey flew back to London on May 31. In England, Kelsey determined that the threat posed to Allied convoys by German air and naval power meant that an aerial ferry route should be established over the North Atlantic so that long-range aircraft could be flown to the United Kingdom rather than shipped. Kelsey spent a month touring British airfields, air groups and aircraft manufacturing facilities, receiving excellent cooperation from Royal Air Force (RAF) personnel. While Spaatz and Hunter remained in England, Kelsey helped a group of war refugees travel to the United States, returning himself to Wright Field as chief of the Pursuit Branch in the Production Engineering Section. In March 1941, Kelsey was promoted to major (temporary). Spitfire evaluation In April 1941, the RAF sent two Spitfire Mark VA fighters to Dayton for testing. The variant used a pressurized cockpit for high-altitude pilot comfort—the pilot would not have to wear an oxygen mask. Kelsey ferried one of the aircraft to and from Los Angeles so that it could be examined further at a California facility. Because of the Spitfire's inherent range limitations, Kelsey was forced to make a number of refueling stops at little-used air fields. Kelsey noted engine overheating during taxiing and brake fade on long desert runways in the presence of significant crosswind. He found long cross-country flight very tiring due to the Spitfire's marginal stability (which gave it high maneuverability in combat.) Kelsey felt that the highly lauded fighter would not have been approved for purchase in the United States where requirements included long range. Drop tanks In November 1941, Kelsey asked his Lockheed contacts to design drop tanks to extend the range of the P-38, even though Air Corps policy at the time was absolutely inflexible toward fighter aircraft carrying external fuel tanks—the so-called Bomber Mafia favoring heavy bombers wanted no challenge from fighters and medium bombers in the long-range department. Lockheed proceeded with the request, starting with a batch of 100 P-38Es intended for photo reconnaissance, despite having no written orders, only Kelsey's handshake. Thus, when combat requirements