Here is the secret document of 1938 that generated the request for the Japanese Zero. (If you weren't bored before, you will be now)
12th Air Corps Secret Document No. 169 of 1938
1. Manoeuvrability of fighter planes is paramount.
2. Proof of results of air raids conducted over Hangzhou & Nanchang.
3. Number of Chinese planes approximately equalled the number of Japanese machines involved.
4. Comparative performance of machines about the same.
5. Chinese pilots lacked skill, manoeuvrability and were of low morale.
6. Chinese pilot skill equalled the Japanese but victory attained by individual manoeuvrability of Japanese pilots.
7. Exceptional pilots involved in prolonged dogfights.
8. Japanese planes lost due to fuel exhaustion.
9. When outnumbered by Chinese planes Japanese pilots achieved victory by use of manoeuvrability.
10. Victories would appear to lie with fighters with most manoeuvrability.
11. Folly to disregard this element.
12. Planes required a sharp turning radius with close agility.
13. Next characteristic long range.
14. Physical time endurance on pilots, questionable fatigue factor.
15. Future aerial engagements up to 32,808 feet altitude.
16. Fighter escort missions in summer over Hankou and Nanchang indicate one-and-a-half-hour flight each way to and from target.
17. Combat altitude anticipated to heights of 22,966 feet.
18. Fighter plane escorts not always possible on long-range bombing mission.
19. 12th Air Corps suggested modified attack-bombers heavily armed.
20. Each escort attack-bomber with a ten-man crew.
21. Each escort attack-bomber will require increase in speed.
22. Faster interceptor speed required.
23. Fighter planes with above characteristics an engineering impossibility.
24. Suggest two distinct fighter plane types:
Carrier fighters
1. Prime flight characteristics must be manoeuvrability. Japanese fighters versus Russian-built I16B Rata (developed from American Boeing P26) in China. Japanese fighters Chinese I16 B 5 min 54 sec to 16,700 ft 6 min 30 sec to 16,400 ft 240 mph max speed 279 mph max speed
2. Time duration for carrier defence estimated at 1½ hours to 2 hours + 20 minutes combat + 1½ hours return to aircraft carrier. Total 3 hours 20 minutes to 3 hours 50 minutes. a. Long hours represent pilot fatigue and reduced efficiency. b. Unfortunately flights limited by inefficient, primitive navigational equipment.
3. Jettisonable fuel tanks a necessity to equal half capacity of the main tanks.
4. Total cruising endurance equal to three and a half to four hours with jettisonable tanks.
5. The maximum level speed may be 12 mph lower than enemy.
6. The combat heights achieved during the Sino-Japanese Incident ranged from 6,562 feet to 22,966 feet. New fighter planes must operate above this height using two-speed or two-stage superchargers.
Land-based fighters
1. Interceptor fighter type required for search sweeps.
2. Maximum speed a primary characteristic to exceed 46 mph, the maximum speed of the enemy bombers.
3. Plane to maintain adequate stability during diving. 4. Range secondary to speed and manoeuvrability.
5. Combat altitude must exceed 32,808 feet.
6. The Chinese bombers dropped bombs from 22,966 feet up as high at 26,247 feet. Future bombing altitude will exceed 32,808 feet.
Armament
1. The bomber armament will increase as the speed.
2. The 7.7 mm machine-gun was considered suitable for defending the bombers up to 656 feet range.
3. Future weapons will require accuracy up to 1,640 feet range.
4. An increase in the initial muzzle velocity will be required.
5. With incendiary bullets enemy may be destroyed up to 656 feet.
6. Hitherto the only way to destroy a bomber was to shoot the pilot or strike fuel tanks
7. Effective range of incendiary bullets will increase using 10 mm or 13 mm weapons.
Special equipment requirements
1. A two-way radio telephone will be required.
2. Pilot’s oxygen apparatus.
3. Electrically heated pilot’s suit.
4. Bomb racks so that fighter may be used for ground strafing.
5. A radio direction-finding and homing apparatus must be installed.
However, no provision appears to have been recommended against enemy fire power, i.e. armour plating or self-sealing fuel tanks
Edwards, Peter J.. The Rise and Fall of the Japanese Imperial Naval Air Service (Kindle Locations 2630-2648). Pen & Sword Books. Kindle Edition.