In WWII, there were several methods for bombers to drop their bombs:
First, there's the famous dive bombing, where the plane dives at a steep angle, often exceeding 45 degrees, sometimes nearly vertical. The bomb is released when the aircraft is very close to the target, followed by a quick pull-up.
However, dive bombing requires high aircraft performance because the stress on the airframe during the dive is significant, necessitating stronger structural design, different aerodynamic considerations, and dive brakes, which can reduce speed and overall performance. Moreover, once a bomber starts its dive, it can't change direction, making it vulnerable to being targeted and shot down by enemy fighters.
Another method is glide bombing, usually employed by fighter-bombers, attack aircraft, or fighters performing ground attacks. The plane enters at a shallow descent angle, levels off near the target to drop the bomb, then pulls up quickly. The Soviet Il-2 attack aircraft often used this technique for ground attacks.
Glide bombing isn't very precise, and the bomb's kinetic energy is lower, but it doesn't demand much from the aircraft's robustness, saves fuel, and is suitable for bombing area targets.
The most common method is level bombing.
Since bombers typically fly at high altitudes, bombs don't fall straight down but follow a parabolic trajectory. Therefore, calculating the bomb release angle is crucial for accurate targeting, involving parameters like airspeed, ground speed, drift angle, wind speed, altitude, and average bomb descent speed.
There was no reliable way to drop bombs with high precision.
However, the U.S. didn't believe this was impossible. Their strategic bombing doctrine focused on high-precision strategic bombing, targeting specific industries or objectives to weaken the enemy's war effort. For example, during the strategic bombing of Germany in WWII, the U.S. concentrated on destroying Germany's fuel and manufacturing industries, with immediate effects.
From a technological standpoint, high-precision bombing requires bombers with long range and heavy payloads, and crucially, a sophisticated bombsight. The U.S. invested heavily in this, spending $1.5 billion to develop the Norden bombsight! This was a massive expense at the time. The total cost of the Manhattan Project was about $3 billion, meaning the Manhattan Project funding could only support two projects like the Norden bombsight, indicating how much the U.S. valued this equipment!
The Norden bombsight, developed by the American company C.L. Norden, consists of two main parts: the stabilizer and the sighting mechanism.
The stabilizer uses a gyroscope to maintain a level platform, providing a stable base for the sighting mechanism. It works in conjunction with the bomber's autopilot to ensure the sight aligns with the flight path.
The most critical part, the sighting mechanism, is the core of the Norden bombsight, comprising three components: a mechanical analog computer for calculating the point of impact, a small telescope, and a system of motors and gyroscopes.
Using the Norden bombsight isn't overly complex. When approaching the target area, the bombardier uses the telescope to locate the target, aided by a set of mirrors. Once the target is centered in the view, the bombardier activates the Norden bombsight. The telescope then keeps the target in view, and the system adjusts its rotation speed based on the target's distance and the aircraft's approach speed. The bombardier must input the aircraft's airspeed and altitude from the instrument panel into the bombsight.
Once set, the bombardier hands control over to the "Norden." At this point, it's not the pilot but the "Norden" that flies the plane along the computed bombing path, making real-time corrections based on the bombardier's final adjustments. When reaching the calculated drop point, the "Norden" automatically releases the bomb, significantly enhancing bombing accuracy. Theoretically, with the "Norden," bombs could be dropped from about 7,000 meters to land within a 30-meter radius of the target.
However, this was just in theory; in practice, such precision was unattainable.
Norden's calculations were based on low-altitude, low-speed bombing, but bombers like the B-17 operated at high altitudes, where the Norden performed poorly. Additionally, the bombardier needed to visually acquire the target, which was not always possible under cloudy conditions, limiting the bombsight's effectiveness.
There's a famous example from 1944 when the Allies bombed a chemical plant in Leuna, covering 757 hectares. In 22 bombing missions with Norden bombsights, 85,000 bombs were dropped, but only 10% hit within the plant area, and 16% of those were duds. Despite heavy bombing, the factory resumed operations within weeks.
Nevertheless, the "Norden" was technically superior for its time, leading the U.S. to treat it as top-secret, with strict security measures like covering it with canvas, installing it only before takeoff, and removing it immediately after landing under armed guard. Crews were sworn to protect its secrecy even at the cost of their lives, and if captured, they were to destroy the "Norden" first.
Ironically, despite these stringent security measures, Germany obtained complete design drawings because one of Norden's German engineers, Hermann Lang, handed over the full set of blueprints to Germany.
Although Germany had the Norden bombsight, like the U.S., it wasn't very effective. Combined with the Luftwaffe's lack of massed strategic bombing capability, it was of little use.
Now, Germany has successfully developed a 3 cm wavelength navigation/bombing radar. With this radar, bombers can achieve bombing accuracy comparable to daylight conditions, even at night or through thick clouds. Night and cloud cover also provide protection against enemy fighter interception and anti-aircraft fire.