We certainly know all about the Doolittle raid, but apparently you don’t as you seem to be confounding it with later bombings raids that actually did damage to Japan. The Doolittle raid was more about morale than anything and did little damage to Japan. It was meant to shake Japan’s confidence in its invulnerability. Since it occurred well before any of the island hopping campaign, it was a small scale carrier based force that was at the outer limits of its effective range (bombers had to land in China after the raid). Larger scale raids did not take place until later in the war, after island bases such as Guadalcanal were occupied. IncreAsing the effectiveness of bombing raids was also much of the impetus behind taking Iwo Jima and Okinawa, since these provided forward bases within range for fighter escorts for the bombers.