Only twenty-two P-40Ds were produced for the USAAF. An order dated February 18, 1941 increased the armament to six guns in the wings, and subsequent aircraft equipped with this armament were designated P-40E (Model 87-B2). The cannon mounts (which were never used in any case) were deleted. Serial numbers of the USAAF P-40Es were 40-358 (c/n 13233), 40-382/681 (c/n 13257/13356), 41-5305/5744, and 41-13521/13599 (c/n 16737/16815).
The P-40E was powered by one 1150 hp Allison V-1710-39 twelve-cylinder Vee liquid cooled engine. Maximum speed was 335 mph at 5000 feet, 345 mph at 10,000 feet, and 362 mph at 15,000 feet. Initial climb rate was 2100 feet per minute. An altitude of 20,000 feet could be attained in 11.5 minutes. Service ceiling was 29,000 feet. Maximum range was 650 miles (clean), 850 miles (with one 43 Imp gal drop tank), 1400 miles (with one 141.5 Imp gal drop tank). Weights were 6350 pounds empty, 8280 pounds normal loaded, and 9200 pounds maximum. Dimensions were wingspan 27 feet 4 inches, length 31 feet 2 inches, height 10 feet 7 inches, and wing area 236 square feet.
There were some attempts in the field to lighten the load of a P-40E so that its performance would be improved. Lt. John Brownewell, a pilot in the 17th Pursuit Squadron removed four of the 6 machine guns in his P-40E, ans well as the oxygen equipment and the radio. A pilot with the 49th Fighter Group instituted just such a modification and found it quite effective. That was George Kiser (9 kills in the PTO) who, in early '42 while flying to defend Darwin, removed the P-40E's two outboard guns and reduced the ammo load in order to reduce weight. It seems likely that this measure was undertaken to reach the 27k foot altitude of the IJN G4M bombers and perhaps to gain some altitude parity with any escorting A6Ms. It also seems likely that Kiser would have probably wanted a wingman flying a plane with the same configuration, given the difference in climb rate his lighter ship would have enjoyed. In addition to Kiser, one pilot flying in the 49th FG, Joe KIng, is reported to have followed Brownewell's example and removed the 4 outboard guns. Apparently. The USAAF ran tests of various versions of a lighter P-40 in Australia. These tests came just a couple of months before the arrival of the P-40K and P-38 in theater. These modifications seem to be pretty extreme measures, and appear to bespeak a desperate concern regarding the equipment on hand to fight the war.
The Kittyhawk IA was essentially the export equivalent of the P-40E. 1500 were built, primarily for the RAF, but many were diverted to Canada, Australia, and New Zealand. Following the passage of the Lend-Lease Act, all aircraft purchased with US funds were required to have standard US designations and had to be issued USAAF serial numbers, even though they were never intended for service with the USAAF. Since the Kittyhawk IA was built with some British equipment, it was not exactly equivalent to the USAAF P-40E, and the Kittyhawk IA was assigned the US designation P-40E-1 (Model 87A-4) to recognize the difference.
The first 20 of the original RAF Kittyhawk order (AK571 to AK590) were equivalent to the USAAF P-40D, but the rest of the order were delivered with 6 wing guns, which made them equivalent to the USAAF P-40E. These were serials AK591 to AK999 and AL100 to AL230, but they were still designated Kittyhawk I by the RAF.
Serials of the Kittyhawk IA:
41-24776/25195 c/n 18795/19214 RAF ET100/ET519 41-35874/36953 c/n 19395/19474 RAF ET520/ET999, EV100/EV699
As mentioned above, many of these Kittyhawk IAs were diverted to Canada, New Zealand, and Australia. Australian serials were A29-1 through A29-163, RCAF serials were 720/731, and New Zealand serials were NZ3001/3044, NZ3091/3098, NZ3100/3180, and NZ3271. However, I don't have any information correlating these serial numbers to RAF serial numbers and back to the USAAF serial numbers.