Enabling Technologies

Advanced USAAF technology made the daylight strategic bombing campaign possible. Key technologies included four-engine bombers, turbosuperchargers, and the Norden bombsight.

Four-Engine Bombers: B-17 Flying Fortress and B-24 Liberator

Four-engine B-17s and B-24s provided the range, payload, defensive armament, and altitude the USAAF required for the strategic bombing campaign in Europe. The US built more than 30,000 B-17s and B-24s and was the only nation in World War II to employ four-engine bombers in a large-scale daytime strategic bombing campaign.

The B-17 was easier to fly, had a higher ceiling, and could take heavier damage than the B-24. Even though it was built in smaller numbers, it was more famous than the B-24.

The B-17 could take punishing damage and still bring its crew back to base.

The B-24 was faster, had longer range, and could carry a heavier bomb load than the B-17. The B-24 was also produced in greater numbers (18,500 B-24s vs 12,700 B-17s)—in fact, more B-24s were built than any other US combat aircraft in history.

Heavy bomber caricatures painted by C. Ross Greening, a pilot and trained artist, while he was a POW in Germany. Earlier in the war, Greening flew on the Doolittle Raid.

Greening depicted the B-17 as a “flying fortress.”

Greening highlighted the slab sides of the B-24 by representing it as a boxcar with wings.

Turbosuperchargers

Turbosuperchargers permitted USAAF heavy bombers to fly at high altitude (20-30,000 feet), where they were less vulnerable to enemy fighters and antiaircraft guns.

The power of a combustion engine is significantly reduced in the low density air at high altitude. Spinning at speeds greater than 20,000 rpm, turbosuperchargers compress intake air, which maintains (or increases) engine power at altitude.

Norden Bombsight

Though not accurate by modern standards, the complex, highly-secret Norden bombsight gave the USAAF a capability unmatched by any other nation at the time. While it could not “drop a bomb in a pickle barrel from 18,000 feet” as famously claimed by a journalist, the Norden could hit large targets like factory complexes from high altitude.

Bombing accuracy with the Norden improved through the course of the war. In 1943, about 20% of the bombs dropped visually by the Eighth Air Force hit within 1,000 feet of the aiming point—by the end of the war, about 50% of the bombs dropped visually hit within 1,000 feet of the target.