Dive bomber

For other uses, see Dive Bomber (disambiguation).

An SBD Dauntless drops its bomb. The dive brakes are extended and are visible behind the wings.

A dive bomber is a bomber aircraft that dives directly at its targets in order to provide greater accuracy for the bomb it drops. Diving towards the target reduces the distance the bomb has to fall, which is the primary factor in determining the accuracy of the drop. Additionally, as the bomb's motion is primarily vertical, the complex parabolic trajectory is reduced to one that is much straighter and easy to calculate - even by eye. The rapid vertical motion of the aircraft also aids it in avoiding fire from anti-aircraft artillery, although diving to low altitude offsets this advantage as it brings the aircraft into range of smaller weapons.

A true dive bomber dives at a steep angle, normally between 45 and 90 degrees, and thus requires a very short pull-up after dropping its bombs. This demands an aircraft of extremely strong construction, and generally limited the class to light bomber designs with ordnance loads in the range of 1,000 lbs. This type of aircraft was most widely used before and during World War II; its use fell into decline shortly afterwards. The most famous examples are the Aichi D3A "Val" dive bomber which sank more Allied warships during World War II than any other Axis aircraft and the Junkers Ju 87 Stuka which was widely used during the opening stages of the war. During pullout, the forces were so great that the crew would often black out, and so the controls of the Ju 87 were automated to avoid loss of the aircraft. This system allowed the Stuka to attack in a steep dive angle and make later pullouts than other aircraft could safely manage, which increased accuracy. Another famous design of the war is the Douglas SBD Dauntless, whose most well known action occurred at the Battle of Midway.

A second and simpler dive bomb technique is to bomb from a much more shallow dive angle, sometimes referred to as glide bombing. Shallower diving angles reduces the benefits in terms of accuracy, but still serves as an aid in keeping the target visible during the bomb run. The Junkers Ju 88 was widely employed in glide bombing and was equipped with special bombsights operated by the pilot for this task. The Heinkel He 177 is often mentioned as having its development upset by the demand that it be able to dive bomb, although this too was an example of glide bombing. Glide bombing should no be confused with the glide bomb, where the bomb glides towards its target while the aircraft remains in level flight. Attachments for this sort of bombing were fitted to examples of the famous Norden bombsight, but in practice this concept proved unworkable.

Technique

Horizontal bombing

When released from an aircraft, a bomb carries with it the aircraft's velocity. In the case of a bomber flying horizontally, the bomb will initially be travelling forward only. This forward motion is opposed by the drag of the air, so the forward motion slows over time. Additionally, gravity provides a constant force on the bomb, accelerating it downward. The combination of these two forces, drag and gravity, results in a pseudo-parabolic trajectory of some complexity. For aiming purposes, the key calculation needed from this trajectory is the distance the bomb will travel forward while it falls, a distance known as the "range". The bomber's task is to fly along a line to the target until it reaches this distance from the target, and drop the bombs at that instant. Even then, if the wind is blowing perpendicular to the line of attack, the bombs will be pushed laterally as they fall, an effect which can be quite extreme, especially from high altitudes. This means that a bombsight or bombardier must be capable of taking the direction and speed of the wind into account as well as the speed of the aircraft and range from target. This is something that is difficult if not impossible to do accurately, at least not on a large and repeatable scale, which led to the Allied bomber forces flying over the target in 1/4 mile-wide formations, and all dropping their bombs together in "strings", theoretically assuring that at least one or two aircraft would drop their bombs onto the target (while ensuring that most of the group wouldn't). This can be thought of as similar to the concept of a machine gun's "cone of fire". It may be difficult to hit a distant and small target with a single aimed shot, but if you fire 100 rounds in a tight pattern around the area of the target, at least one round will likely hit the target. While this technique of bombing leads to large areas of destruction and makes the task of hitting only a single building essentially impossible, it does however mean that the bombs won't be scattered over a random area of the city, increasing the likelihood of hitting the specified target. In practice, weather, the stress of combat, human errors and mechanical errors all contributed to decreasing the accuracy of "precision" bombing. Successful degradation of targets was largely in consequence to the large number of aircraft in the raids, repetitively targeting the objective, and the large numbers of bombs dropped.

In the past, aircraft did not have navigation systems that could direct an aircraft towards an arbitrary point in space. Instead, navigation was carried out in relation to objects on the ground - whether they be visual indications or radio beacons. If one calculates the range for a given set of conditions, simply trigonometry can be used to find the angle between the aircraft and the target when they are that far apart. By setting the bombsight to that angle, the "range angle", the aircraft simply had to approach the target and drop its bombs when the target appeared lined up with the sights. This was only effective for "area bombing", however, since radio equipment wasn't accurate or powerful enough to specify a specific target. Large formations could drop bombs on an area hoping to hit a specific target in the dark, but there was no guarantee and huge areas around the target would be demolished, even worse than with "precision" bombing.

As the trajectory of the bomb is complex, solving the range is a complex problem. This is normally accomplished by looking up data measured on a bombing range and reduced into table form. Any changes in speed, direction or altitude required all of this to be looked up again. In order to reduce this workload, mechanical calculators were increasingly common during World War II, including the famous Norden bombsight and the less well known British Mark XIV bomb sight and German Lotfernrohr 7. Even with these calculators, accuracy was often poor due to inaccuracies in the ballistics of individual bombs, wind measurements, or setup errors. Moreover, the need to fly in a straight line toward the target made it easy for anti-aircraft artillery to aim at the bomber, which demanded that the aircraft fly higher to avoid fire, and thereby magnified any errors in setup. In spite of enormous efforts, accuracies for horizontal bombing throughout the war was generally measured in thousands of yards. All these points meant that the horizontal bomber was ill-suited for tactical bombing, particularly in close support. To hit any one target, relatively large numbers of bombers and bombs were needed, which were difficult to communicate with in real-time, and which took time to organize and send after a target (which may or may not be obstructed by cloud when they arrived). When they did attempt to bomb a target, the large dispersion and aiming inaccuracies meant that anything within a mile of the target was in danger. Attempts at using high-altitude bombing in near-proximity to troops often ended up in tragedy, with the bombs dropped on "friendly" troops, as well as the enemy. In attacking shipping, the problems of inaccuracy were amplified by the fact that the target was usually moving, and could change its direction between the time the bombs were released and the time they arrived. Thus, the horizontal bomber was of limited use in attacking shipping. Successful strikes on marine vessels by horizontal bombers were extremely rare. An example of this problem can be seen in the attempts to attack the Japanese carriers using B-17s at altitude early in the battle of Midway. No hits were scored. The German battleship Tirpitz was subjected to countless strikes, many while in dock and immobile, and wasn't successfully sunk until the British brought in special, enormous bombs to ensure that even a near miss would do the trick.

Dive bombing

Consider the same aircraft, now traveling vertically instead of horizontally. In this case there is no horizontal velocity when the bomb is dropped, so the force of gravity simply increases the speed along the existing vertical trajectory. The bomb will travel in a straight line between release and impact, eliminating all of the complex calculation and setup required in the bombsight. Instead, the aircraft can simply point itself directly at the target and release the bombs, the only source of error being the effects of winds after release. For bombs, which are well streamlined and relatively dense, wind has a very small effect, and the bomb is likely to fall within its lethal radius of the target.

Diving perfectly vertically is by no means simple, especially when considering the forces generated when the aircraft has to return to horizontal flight after the drop. But more generally, as the aircraft tilts further from the horizontal, the horizontal component of its own airspeed is reduced, which reduces the range. At some point, for a given altitude and dive angle, the trajectory so closely matches a straight line that bomb sighting becomes a trivial exercise and a straight line sight is all that is needed. Differences in the path due to the ballistics of different bombs can be accounted for by selecting a standardized bombing altitude and then adjusting the dive angle slightly for these different cases.

In these examples, accuracy of the drop is primarily a function of the pilot or bombardier's ability to accurately sight the target. This is aided by the fact that the aircraft is pointed towards it, making sighting over the nose dramatically easier. In addition, the target continues to approach as the bomber dives, allowing the aim to be progressively adjusted over time. In comparison, if a horizontal bomber notices that it is off the line directly over the target when the range angle is reached, there is nothing they can do - turning to the angle that would correct this would also change the groundspeed of the aircraft (at least in the presence of wind) and thereby change the range as well.

For this reason, dive bombing was the only method of providing the accuracy needed to attack high-value point targets like bridges and ships. They were a common feature of most naval air services, and many land-based air forces as well.

On the negative side, optimizing an aircraft for near-vertical dives came at the expense of performance. During normal horizontal flight, a typical aircraft is in balance between the lift its wings and tail generate, gravity, the force of its engine and drag. When it is put into a near vertical dive, the lift from the wings and horizontal tail are no longer balanced and cause the aircraft to return to level flight, tracking across the target unless the pilot applies considerable force to keep the nose down, with a corresponding decrease in accuracy (meaning that while the nose is pointed straight down, the wings are still trying to "lift" the aircraft. Since there is no longer gravity counteracting this, the aircraft will have a tendency to fly "up" while in a dive, moving it across the target as it dives, rather than straight down). To compensate for this, many dive bombers were designed to be trimmed out, either through the use of special dive flaps (such as Fairey Youngman flaps) or through changes in tailplane trim that must be readjusted when the dive is completed. The Vultee A-31 Vengeance was designed to be trimmed for diving, at the expense of addition drag while in level flight. Failure to re-adjust trim often made the aircraft difficult or impossible to pull out of a dive. In addition, a dive bomber was vulnerable to low-level ground fire as it dived towards its target since it was often headed in a straight line directly towards the defenders. At higher levels this was less of a problem, as larger AA shells are fused to explode at a certain altitude, which is almost impossible to predict accurately while the plane is diving towards the gunner. In addition, most higher-altitude gunners and gunnery systems were designed to calculate the lateral movement of a target; while diving, the target appears almost stationary. Also, many AA mounts lacked the ability to fire directly up, so dive bombers were almost never exposed to fire from directly ahead, and there were few gunners who could accurately keep their positions and put up effective fire while a group of bombers dived towards them; the natural tendency is to panic and seek cover. Dive brakes were employed on many designs to create drag which slowed the aircraft somewhat in order to increase accuracy and to prevent speeds which could damage the structure of the aircraft. When introduced these were almost exclusive to dive bombers, though the air brakes fitted to modern aircraft function in a similar manner.

History

World War I and inter-war period

The Aichi D1A2, a carrier-borne dive bomber.

The first recorded use of dive bombing was an ad-hoc solution by British Royal Flying Corps pilots during World War I. In 1917 and 1918, they practised the technique at the Orford Ness Bombing Range.

In 1919 United States Marine Corps pilot Lt. L. H. Sanderson mounted a carbine barrel in front of the windshield of his Curtiss JN-4 (a training aircraft) as an improvised bomb sight, loaded a bomb in a canvas bag attached to the plane's underside, and made a solo attack in support of US Marines trapped by Haitians during the United States occupation of Haiti. Sanderson's bomb hit its target precisely and the raids were repeated. During 1920 Sanderson familiarized aviators of USMC units at the Atlantic coast with the dive bombing technique. Dive bombing was also used during the United States occupation of Nicaragua.

Interwar era

As planes grew in strength and load capability, the technique became more valuable. By the early 1930s it was clearly favoured in tactical doctrine, notably against targets that would otherwise be too small to hit with level bombers. In the 1920s the US Navy ordered the first custom dive bomber aircraft, the Curtiss F8C Hell-Diver biplane (not to be confused with the later SB2C Helldiver). The Imperial Japanese Navy followed by ordering the Heinkel He 50 in 1931, which they developed into their own Aichi D1A. Numerous examples followed, including the US Curtiss SBC, Japanese Aichi D3A and others. Because navies operated from aircraft carriers or small airfields, they had "smaller numbers of aircraft available for any one attack, and each aircraft was often unable to carry more than a few bombs per plane." They also were frequently required to attack smaller-sized or moving targets, such as ships. The combination of a small bomb load and the need for accuracy made dive bombing techniques a requirement for naval airplanes.

Land-based forces proved generally less interested in the dive bomber role. Accurate bombardment of point targets at long distances did not appear to be a military requirement, and at shorter ranges artillery could already fill any demand. Development concentrated primary on ground attack aircraft, which were intended to attack primarily with guns and cannon against infantry and light armour. Examples include the Fairey Battle, Henschel Hs 129 and Ilyushin Il-2. However, Luftwaffe experience in Spain demonstrated the value of the dive bombing technique, repeatedly attacking high value targets and causing damage to the enemy out of proportion to the size of the force. This led to the famed Junkers Ju 87, and in turn, to many other air forces starting dive bomber efforts of their own.

One notable holdout was the US Army Air Corps (USAAC). In the 1930s a new generation of bombsights like the Norden were being introduced, which suggested that level bombers could attain accuracies somewhat similar that those of the dive bombers. Although the accuracy would not be as great, an aircraft flying horizontally would not be subject to the great stresses of diving, and could be built to hold a dramatically greater warload. Thus, any loss of accuracy could be made up by carrying more bombs, increasing the chance that one would hit. Moreover, this aircraft would also be able to fly at high altitude throughout the attack, greatly increasing its odds of surviving. This thinking led to a great debate in military aviation circles. The US Navy, developing the Norden, made plans for most of its new aircraft to be able to level bomb. However, they also continued development of dive bombers and torpedo bombers, as the best method of attacking ships was not clear at that time. The USAAC confidentially predicted that the Norden would allow it to attack ships with ease, and designed their strategy around long-range bombers like the Boeing B-17 Flying Fortress which would be able to counter any seaborne attack at long range. Work on dive bombers and attack aircraft was scaled back dramatically.

World War II

The only major force not to deploy a dedicated dive bomber were the inventors of the tactic, the British. The Royal Navy attempted to introduce their own on several occasions, but were never able to do so due to various reasons, not the least of which was political interference by the RAF. They only produced hybrid aircraft: the Blackburn Skua, a dive bomber/fighter that was used for a short time and in small numbers, and the Fairey Barracuda, a dive bomber/torpedo bomber. However, the Skua sank the German cruiser Königsberg by dive bombing - the first time ever that a major warship was sunk in combat by air attack.

European theater

Stukas during action, Eastern Front

In the early 1930s, Ernst Udet visited the U.S. and was able to purchase four F8Cs and ship them to Germany, where they caused a minor revolution. The dive bombing technique would allow a much smaller Luftwaffe to operate effectively in the tactical role. Soon they had sent out contracts for their own dive bomber designs, resulting in the gull-winged Junkers Ju 87 Stuka (a contraction of Sturzkampfflugzeug, literally "diving combat airplane").

When it was introduced in 1936, the Stuka was the most advanced dive bomber in the world. Using it as "aerial artillery" solved a major problem in the concept of Blitzkrieg—how to attack dug-in defensive positions. Normally this would require slow-moving artillery to be used, making the fast moving armoured forces wait for it to catch up. Close coordination between the ground forces and Stukas could achieve the same ends, on the move.

This was proven to great effect during the invasion of Poland and the Low Countries. In one particular example, the British Expeditionary Force set up strong defensive positions on the west bank of the Oise River just in front of the rapidly advancing German armour. Attacks by Stukas quickly broke the defence, and combat engineers were able to force a crossing long before the artillery arrived. Another important example was the massive aerial attacks in 13 May 1940 against strong French defence positions at Sedan in the Battle of France, which allowed the German forces a fast and (for the Allies) unexpected breakthrough through the French lines, eventually leading to the German advance to the Channel and the cutting off of large parts of the Allied army.

Despite its success in the French campaign, the Stuka soon showed its weaknesses in the Battle of Britain where great numbers of Stukas were lost due to its inappropriate use as a tactical bomber. In this case the lack of air superiority meant that the slow-moving aircraft was also at great risk to attack by fighters. This had not been the case in earlier battles, where the Luftwaffe maintained air superiority throughout.

The Stuka was the only widely used dedicated tactical dive bomber to be deployed against both naval and land targets, particularly with regard to the latter in the anti-armor role. Stukas also had 7.92mm machine guns or 20mm cannons mounted in the wings, with some modified to have 37mm cannons mounted below the wings for anti-tank work. With the loss of Luftwaffe air superiority in the east they became vulnerable to the Red Army Air Force fighters, and from 1943 had begun conversion to the more conventional cannon attack tactics.

The Royal Navy's Barracudas made several attacks on the German battleship Tirpitz in 1944. The first (Operation Tungsten) was the most successful and put the ship out of action for 2–3 months.

The most successful dive bomber in history was Hans-Ulrich Rudel who in 2,300 combat sorties destroyed a battleship, a cruiser, two destroyers, over 500 tanks, and a number of aircraft. Rudel, who survived the war, eventually co-wrote a book about his experiences and consulted with the US Air Force. Although dogfighting and air superiority created more 'household names,' the sheer volume of Rudel's destruction does not appear to be challenged by any fighter ace or tank ace, perhaps making him one of the most significant fighters in history.

Pacific theater

United States Navy Curtiss SB2C Helldiver dive bomber

Both the Imperial Japanese Navy (IJN) and the U.S. Navy invested considerable effort on dive bombers. Japan started the war with a very good design, the Imperial Navy's carrier-borne Aichi D3A ("Val"). As the war progressed the design became outdated due to its limited speed, due in part to the limited horsepower of its power plant and to the greater drag of its fixed main landing gear (a shortcoming shared by the Stuka). Later, when the IJN was on the defensive, the more advanced Yokosuka D4Y Suisei entered service. By then, Japan's industrial output had dropped and production levels were limited.

The U.S. initially fielded the Douglas SBD Dauntless, which was similar to the D3A in performance. Later in the war the Dauntless was replaced with the faster, but more complex and trouble prone Curtiss SB2C Helldiver. As was usual with US war industry during WWII, both airplanes were built in large numbers.

The IJN's dive bombing moment of success was during their Indian Ocean Raids in April 1942, and the Japanese carriers launched strikes against the British navy's battle squadrons stationed near Ceylon and India, and Aichi D3As sank the Royal Navy aircraft carrier HMS Hermes and the heavy cruisers HMS Cornwall and HMS Dorsetshire, along with the escorting destroyer HMS Vampire.

A pivotal example of successful naval dive-bombing attacks took place in the decisive Battle of Midway in June 1942 when American Dauntlesses scored fatal hits on three Japanese aircraft carriers within a six minute timespan. Within hours the Imperial Japanese Navy had lost a major part of its battle fleet and many experienced naval airmen, both of which Japan would have difficulty in replacing.

Decline

Even during World War II, the dive bomber class began to disappear. Anti-aircraft defences - both fixed gunnery positions and fighter interception guided by radar - had improved. At the same time new computing bomb sights allowed for better accuracy from smaller dive angles, and the sights could be fitted to almost any aircraft, including fighter bombers, improving the effectiveness of ground-attack aircraft.

The RAF came to regret its dislike of the dive bomber when the Desert Air Force found its aircraft to be impotent against the Panzers of [[Erwin Rommel]`s Afrika Korps, in early 1942. Henry Tizard Chief Scientist to the British Government formed a panel of experts, which suggested the use of rockets. With a speed of 1,000 mph a rocket has a much flatter trajectory than a bomb. So it could be launched reasonably accurately from a shallow dive.

The British Army had used rockets to fire against low-flying bombers during the Battle of Britain and by enlarging the tube from 2 inches to 3 inches and fitting first a 28 pound and then a 60 pound high explosive warhead, a new weapon was quickly developed.

Russian assistance was requested as they were already using rockets against German tanks, but in spite of receiving a gift of Hawker Hurricanes none was given. The British fitted them initially to Hurricanes in June, 1942 in time to deploy them against Rommel`s tanks.

The Hawker Typhoon originally developed as a fighter replacement for the Hurricane proved more effective as a ground attack fighter. It could carry two 1,000 pound bombs, when it entered service in September 1942 and a year later could carry eight RP3 60 pound rockets , providing the same impact as a naval destroyer`s broadside.

On May 23 1943 a Fairey Swordfish destroyed U752 in the Atlantic and five days later a Lockheed Hudson of RAF Coastal Command destroyed another U-boat in the Mediterranean. These rockets were fitted with iron spikes and fired at a shallow angle into the sea. Once under water, they curved upwards and punctured the hull below the waterline, making it impossible for a submarine to submerge.

Caltech developed the 5 inch High Velocity Aircraft Rocket better known as Holy Moses with a 24 pound warhead for the US Navy. It was rushed to Europe for use on D-Day and later used by Navy planes in the Pacific.

By January 1943, American pilots who had been flying in the RAF Eagle Squadrons before the US entered the war were converting from Supermarine Spitfires to Republic P47 Thunderbolts to form the 4th Air Fighter Group of the USAAF in England. At over 4 tons unladen , one of the biggest single engine fighter bombers of the war, it could carry five 500 pound bombs or ten 5 inch HVARs in its increasingly useful ground-attack role.

By late 1944, the RAF was able to hit moored ships from great heights inflicting far more damage at less risk than with a dive bomb. Two 5 tonne Tallboy bombs dropped by Avro Lancasters from 25,000 ft hit at supersonic speed and capsized the German battleship Tirpitz on November 12 1944. The Lancasters were from the specially recruited and trained 617 squadron, often known as the Dambusters, under Wing Commander Guy Gibson. The [[Tallboy]} was developed by Vickers aircraft designer Barnes Wallis who also designed two versions of a bomb that bounced on water. . US pilots in the Pacific developed a technique of skip bombing which required flying at low level and dropping a spherically-nosed conventional bomb onto the sea, at a shallow angle, which then bounced back into the air.

Although aircraft still dived on their targets, they were no longer optimized for steep diving attacks at the expense of other capabilities. As the Hawker Typhoon and Republic P47 Thunderbolt were capable of many other missions, they were not called dive bombers. Shallow, 45° or less dive bombing attacks are still used to deliver gravity bombs when they are employed, although this is primarily to keep the target in view .

After pioneering efforts in World War II by both the Luftwaffe with the Fritz X, and the USAAF with the Azon controlled-trajectory bombs, today's smart bombs have largely reduced the need for dedicated attack platforms. Bombs can be dropped far from the target's defences, minimizing risk to the aircraft. The bomb is then guided or guides itself onto the target through a number of means, ensuring far greater accuracy.

Bomb sights provide "toss bombing" modes, a sort of reverse dive bombing where an aircraft pulls up from low level before releasing the bombs.

References

Notes

Citations

Bibliography

• Angelucci, Enzo and Paolo Matricardi. World Aircraft: World War II. Volume II (Sampson Low Guides). Maidenhead, UK: Sampson Low, 1978. ISBN 0-562-00096-8.
• Brown, David. Warship Losses of World War II. Arms and Armour, London, Great Britain, 1990. ISBN 0-85368-802-8.
• Casey, Louis. Naval Aircraft. Secaucus, New Jersey: Chartwell Books Inc. 1977. ISBN 0-7026-0025-3.
• Parshall, Jonathan (2005). Shattered Sword: The Untold Story of the Battle of Midway. Dulles, Virginia: Potomac Books. ISBN 1-57488-923-0. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help) Uses recently translated Japanese sources.
• Worth, Richard. Fleets of the World War II. New York: Da Capo Press, 2001. ISBN 978-0-306-81116-6.

External links

• "Dive Bombing at Target Assures Accuracy" April 1933, Popular Mechanics - early article on dive bombing for general public
• "Diving Artillery" , April 1942, Popular Science good article on the basics of dive bombing with illustration and rare photos
• Tail Brake on Do-217E Controls Its Diving Speed, November 1942, Popular Science
• battle Dive bombers compared Flight article of 1940