Dive bomber
A dive bomber is a tactical bomber aircraft that attacks its target by performing fast dives in order to provide greater accuracy for the aerial bomb it drops. Diving directly towards the target before releasing gives the bomb a faster overall speed and a greater terminal momentum, straightens the bomb's free-fall trajectory, and allows the pilot to keep visual contact throughout the bomb run. This allows more focused attacks on point targets and ships, which were difficult to attack with conventional level bombers even en masse.
Dive bombers are typically light bombers or fighter-bombers with great aerial agility, and were especially effective against vehicles early in World War II when Nazi Germany's combined arms doctrine integrated the Luftwaffe into the Blitzkrieg. After World War II, the rise of precision-guided munitions and improved anti-aircraft defences—both fixed gunnery positions and fighter interception—led to a fundamental change in dive bombing. New weapons, such as rockets, allowed for better accuracy from smaller dive angles and from greater distances. They could be fitted to almost any aircraft, including fighters, improving their effectiveness without the inherent vulnerabilities of dive bombers, which needed air superiority to operate effectively.
Method
A dive bomber dives at a steep angle, normally between 45 and 60 degrees or even up to a near vertical dive of 80 degrees with the Junkers Ju 87, and thus requires an abrupt pull-up after dropping its bombs. This puts great strains on both the pilot and aircraft. It demands an aircraft of strong construction, with some means to slow its dive. This limited the class to light bomber designs with ordnance loads in the range of although there were larger examples.The most famous examples are the Junkers Ju 87 Stuka, which was widely used during the opening stages of World War II often accompanied with the screaming sound of its sirens, the Aichi D3A "Val" dive bomber, which sank more Allied warships during the war than any other Axis aircraft, and the Douglas SBD Dauntless, which sank more Japanese ships than any other allied aircraft type. The SBD Dauntless helped win the Battle of Midway, was instrumental in the victory at the Battle of the Coral Sea, and fought in every US battle involving carrier aircraft.
File:SBD Dauntless El Segundo.JPG|thumb|left|Final assembly view of SBD Dauntless dive bombers in 1943 at the Douglas Aircraft Company plant in El Segundo, California. The dive brakes are visible behind the wings.
An alternative technique, glide-bombing, allowed the use of heavier aircraft, which faced far greater difficulties in recovering from near-vertical approaches, though it required greater use of sophisticated bombsights and aiming techniques, by a specialised member of aircrews, namely a bombardier/bomb aimer. The crews of multi-engined dive-bombers, such as variants of the Junkers Ju 88 and Petlyakov Pe-2, frequently used this technique. The heaviest aircraft to have dive-bombing included in its design and development, the twin engine Heinkel He 177, also utilised a glide-bombing approach; the requirement that the He 177 be able to dive/glide-bomb delayed its development and impaired its overall performance.
Dive bombing was most widely used before and during World War II; its use declined during the war, when its vulnerability to enemy fighters became apparent. In the post-war era, this role was replaced with a combination of improved and automated bombsights, larger weapons and even nuclear warheads that greatly reduced the need for accuracy, and finally by precision guided weapons as they became available in the 1960s. Most tactical aircraft today allow bombing in shallow dives to keep the target visible, but true dive bombers have not been a part of military forces since the start of the jet age.
Accuracy
When released from an aircraft, a bomb carries with it the aircraft's trajectory. In the case of a bomber flying horizontally, the bomb will initially only be travelling forward. This forward motion is opposed by the drag of the air, so the forward motion decreases over time. Additionally, gravity causes the bomb to accelerate after it is dropped. The combination of these two forces, drag and gravity, results in a complex pseudo-parabolic trajectory.The distance that the bomb moves forward while it falls is known as its range. If the range for a given set of conditions is calculated, simple trigonometry can be used to find the angle between the aircraft and the target. By setting the bombsight to this "range angle", the aircraft can time the drop of its bombs at the instant when the target is lined up in the sight. This was only effective for "area bombing", however, since the path of the bomb is only roughly estimated. Large formations could drop bombs on an area hoping to hit a specific target, but there was no guarantee of success, and huge areas around the target would also be hit. The advantage to this approach, however, was that it is easy to build such an aircraft and fly it at high altitude, keeping it out of range of ground-based defences.
The horizontal bomber was thus ill-suited for tactical bombing, particularly in close support. Attempts at using high-altitude bombing in near-proximity to troops often ended in tragedy, with bombs both hitting their targets and friendly troops indiscriminately. In attacking shipping, the problems of inaccuracy were amplified by the fact that the target could be moving, and could change its direction between the time that the bombs were released and the time that they arrived. 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 in the Battle of Midway, with no hits scored. The German battleship Tirpitz was subjected to countless attacks, many while in dock and immobile, but was not sunk until the British brought in enormous Tallboy bombs to ensure that even a near miss would be effective.
An aircraft diving vertically minimises its horizontal velocity component. When the bomb is dropped, the force of gravity simply increases its speed along its nearly vertical trajectory. The bomb travels a virtually straight line between release and impact, eliminating the need for complex calculations. The aircraft simply aims at the target and releases its bombs. The primary source of error is the effect of wind on the bomb's flight path after release. As bombs are streamlined and heavy, wind has only a slight effect on them and the bomb is likely to fall within its lethal radius of the target.
Bomb sighting becomes trivial, requiring only a straight line of sight to the target. This was simplified as the aircraft was pointed directly at the target, making sighting over the nose much easier. Differences in the path of different bombs due to differing ballistics can be corrected by selecting a standardised bombing altitude and then adjusting the dive angle slightly for each case. As the bomber dives, the aim could be continually adjusted. In contrast, when a horizontal bomber veers offline while approaching the bomb release point, turning to the angle that would correct this also changes the speed of the aircraft over the ground and thereby changes the range as well.
In the 1930s and early 1940s, dive bombing was the best method for attacking high-value compact targets, like bridges and ships, with accuracy. The forces generated when the aircraft levels out at the bottom of the dive are considerable. The drawback of modifying and strengthening an aircraft for near-vertical dives was the loss of performance. Aside from the greater strength requirements, during normal horizontal flight, aircraft are normally designed to return to fly straight and level, but when put into a dive the changes in forces affecting the aircraft now cause the aircraft to track across the target unless the pilot applies considerable force to keep the nose down, with a corresponding decrease in accuracy. To compensate, many dive bombers were designed to be trimmed out, either through the use of special dive flaps or through changes in tailplane trim that must be readjusted when the dive is completed.
The Vultee Vengeance, which was mostly used by the RAF and RAAF in Burma, was designed to be trimmed for diving, with no lift to distort the dive. The drawback was that it flew nose up in level flight, increasing drag. Failure to re-adjust trim made the aircraft difficult or impossible to pull out of a dive.
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 were fused to explode at specific altitudes, which is impossible to determine while the plane is diving. 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.
Dive brakes were employed on many designs to create drag which slowed the aircraft in its dive and increased accuracy. Air brakes on modern aircraft function in a similar manner in bleeding off excessive speed.
Origins
It is difficult to establish how dive bombing originated. During World War I, the Royal Flying Corps found its biplane two-seat bombers insufficiently accurate in operations on the Western Front. Commanders urged pilots to dive from their cruising altitude to under to have a better chance of hitting small targets, such as gun emplacements and trenches. As this exposed the aircraft and crew to destructive ground fire in their unprotected open cockpits, few followed this order. Some recorded altitude at the top and bottom of their dive in log books and in squadron records, but not the steepness of the dive. It was certainly not near-vertical, as these early aircraft could not withstand the stresses of a sustained vertical dive.The Royal Naval Air Service was bombing the Zeppelin sheds in Germany and in occupied Belgium and found it worthwhile to dive onto these sheds to ensure a hit, despite the increased casualties from ground fire. Again, the angle of dive in these attacks was not recorded.
Beginning on 18 June 1918, the Royal Air Force, successor to the RFC, ordered large numbers of the Sopwith TF.2 Salamander, a single-seat biplane. The "TF" stood for "Trench Fighter", and the aircraft was designed to attack enemy trenches both with Vickers.303 machine guns and with bombs. Of the 37 Salamanders produced before the end of October 1918, only two were delivered to France, and the war ended before those saw action. Whether the Salamander counts in more modern parlance as a fighter-bomber or as a dive bomber depends on the definition of "dive". It had armoured protection for the pilot and a fuel system to attack at low level, but lacked dive brakes for a vertical dive.
Heavy casualties resulting from air-to-ground attack on trenches set the minds of senior officers in the newly formed RAF against dive bombing. So not until 1934 did the Air Ministry issue specifications for both land-based and aircraft carrier-based dive bombers. The RAF cancelled its requirement and relegated the Hawker Henley dive bomber to other roles, while the Fleet Air Arm's Blackburn Skua was expected to do double duty: as a fighter when out of reach of land-based fighter support, and as a dive bomber. It had dive brakes that doubled as flaps for carrier landings. The Hawker Henley had a top speed only slower than the Hawker Hurricane fighter from which it was derived. The American and Japanese navies and the Luftwaffe chose vertical dive bombers whose low speed had dire consequences when they encountered modern fighters.