Why more Japanese heavy AA guns would not solve air defence

What if Japan began building a unified heavy anti-aircraft network for the home islands and occupied territories in 1939?

It would inflict more bomber losses, but guns alone could not compensate for finite resources, weak implementation, and Japan's shortage of trained replacement pilots.

More Type 5 15 cm and Type 3 12 cm anti-aircraft guns would shoot down additional bombers, but a large fixed-defence programme would compete with other military needs. The football analogy assigns bombers the task of attacking enemy airfields, fighters the job of intercepting aircraft across the field, and heavy AA guns the defensive line. Short-range local weapons act as the goalkeepers. Increasing one layer's resources can leave fewer aircraft or weapons in the others because the budget is finite. Japan's problem also includes the early loss of skilled pilots and too few replacements to sustain the air war.