1. Supermarine Spitfire (United Kingdom):
- Early variants (1936-1941): 2,500-4,000 man-hours
- Later variants (1942-1945): around 1,500-2,000 man-hours
2. North American P-51 Mustang (United States):
- Early variants (1941-1943): 6,500-7,500 man-hours
- Later variants (1943-1945): 3,500-4,500 man-hours
3. Messerschmitt Bf 109 (Germany):
- Early variants (1935-1941): 3,000-4,000 man-hours
- Later variants (1942-1945): around 2,500-3,500 man-hours
4. Mitsubishi A6M Zero (Japan):
- Early variants (1940-1942): 4,000-5,500 man-hours
- Later variants (1943-1945): around 3,000-4,000 man-hours
It's worth noting that these estimates can differ based on the specific variant, production facility, wartime disruptions, and other factors. Improvements in production techniques, such as the use of sub-assemblies and increased standardization, led to significant reductions in assembly times as the war progressed.