I was just wondering why it takes so long to build modern combat aircrafts that the maximum that are built are at the rate of about 20 a year or so in advanced countries. In India the Su30 MKI is being produced at 12 a year with all the modern technologies available. Compare it with the WWII era aircrafts which were mass produced like we produce cars today. Some examples are as below. Bf-109:- 33,984 in 8 years Spitfire:- 20,351 in 10 years P-51 :- 16,766 in 8 years B-29 :- 3970 in 3 years Lancaster Bomber 7377 in 6 years All the above were some of the most successful birds of all times. Did a great job for their respective operators. One argument that will be put forth is that so many were required so they were produced in large numbers during the war. Yes but a "small" order of 250 MKIs is going to take us a dozen years!! The production rate of WWII fighters was a staggering at about 4000 a year for the Bf 109 and 2000 a year for the spitfire.