In wartime, the B-29 was capable of flight up to 40,000 feet (12,000 m), at speeds of up to 350 mph (true airspeed). This was its best defense, because Japanese fighters of that day could barely get that high, and few could catch the B-29, even if they were at altitude and waiting. Only the heaviest of anti-aircraft weapons could reach it, and since the Axis forces did not have proximity fuzes, hitting or damaging the airplane from the ground in combat was next to impossible.