Why were roads in 1930s Japan poor quality?
Horikoshi says that he saw a German engineer was leading a team on his first day at Mitsubishi, says he was sent to Europe by Mitsubishi to learn from European manufacturers, says that the Navy would buy Mitsubishi data from European manufacturers, etc. - how did Europe get so far ahead in such a short time and what did these business relationships look like?
Horikoshi apparently had a startmonth at Mitsubishi, rather than a startdate - was it common for Japanese companies to not care when new employees showed up?
Why was Horikoshi selected to design the Mitsubishi 1MF10?
Why was the Japanese Navy providing air support for ground troops during the Second Sino-Japanese War, rather than the Army? Why did the Navy need land-based planes?
Had any previous engineers tried to make control surfaces have a proportional response?
Horikoshi stated that he opted for a more manpower-intensive design over a resource-intensive, whenever forced to choose, while every Western power except Britain chose the opposite - why did Britain also choose more manpower-intensive designs? (Or did they not?)
What metals were other makers using at the time and how did they compare to duralumin?
Did Japan have self-sealing fuel tank technology, at the time?
The Navy was apparently very secretive regarding air battles during the Second Sino-Japanese War; was this a general policy in Imperial Japan? If not, why?
What were Japanese citizens' attitudes towards the war?
What were Japanese citizens' attitudes to becoming allies with Nazi Germany?
Horikoshi states that he knew immediately that Japan lacked the industrial might to fight a prolonged war with a major power; was this a common thought among the educated class, during WWII? Why did the military and political leadership disagree?
Where there any notable engineers and designs at other Japanese companies in this period?
I'll answer the questions that I actually know.
Q2. What do you mean by far ahead? If you're referring to aviation, it's mainly because the post-WWI period saw quite a lot of experimental aircraft being designed in both military and civilian usages where military air arms were established in France, Germany, Britain, and the US among other countries. The other thing to remember is that Japan by 1930 had been a developed industrial nation for all of about 40 years. France, Britain and Germany had developed more than just reconnaissance air forces in WWI compared to Japan which had done little with regards to airpower until around the 1920s.
A lot of the business relationships were literally purchases of blueprints coupled with a model. In other cases Japanese technicians and engineers in the late 1910s and early 20s copied and studied foreign designs and basically prototyped their own version based off of design cues.
Q5. The IJA and IJN are...a curious entity. What's probably more surprising is that they had cooperation during the Second Sino-Japanese War, but the IJN needed land based in order to extend range and because carriers had limited operational capacity. Logistically it made sense considering that the IJN's range could be extended inland via land based planes. Note that the IJN did not operate entirely on water as they also had a standing army.
Q6: An interesting question, I'm not actually sure as my research on control surfaces are a bit limited.
Q7: Britain did and did not. It very much depended on the plane. I'm assuming that Horikoshi is referring to the duraluminum composition of the Spitfire and the geodesic wood/duraluminum frame of the Vickers Wellington and Wellsey which were indeed labor intensive. That said the British also designed the De Havilland Mosquito and Hawker Hurricane, both of which were wood frame based planes that did not require as intricate of a design. However I'm not convinced that other manufacturers really saved that much manpower or resources considering that almost all plane designs (even the late war German ones) required a significant amount of time, metals, manpower and expertise. For example the P-51 Mustang's laminar flow wing required a higher degree of finish and precision due to the lower tolerances of the design itself.
Perhaps the fit and finish of later war planes in Germany or the fit and finish of early Russian planes may have been poor, but to say that they were necessarily cheap or easy to produce only works on relative scales. Even then I wouldn't say that any country opted for a general philosophy of less or more resource intensive.
Q8. Most planes used a variation of aluminum alloys that are now all generally referred to as duraluminum. Some might have used different types of aluminium but for the most part planes either used aluminium variants or chemically treated wood.
Q9. Specifically when? By the late 1930s they definitely had it though there was an intentional reason to exclude it from Japanese designs. Note that most of their late-30s designs specifically the Ki-43 and A6M were planes designed for both manueverability and range. Though self-sealing fuel tanks were useful, the lack of armor on those planes and the extra weight were seen as superfluous at the time for fighter planes.
Q13. Military leadership was aware that Japanese industrial power could not fight a prolonged war. Recall Yanmamoto's reasoning for attacking Pearl Harbor. Though it backfired, the understanding that Japan lacked the resources for protracted war against the United States was very much known since the late 1930s.
Q14. I will get back to you on this one.