Naval Anti-Aircraft Guns and Gunnery. Norman Friedman
their light bombs (20 or 30lbs each). The British Fleet Air Arm continued to develop such tactics, which it called convergence attacks, after the war. The US Marine Corps became interested in this form of precision attack, presumably due to its experience in counterinsurgency in Central America and the Caribbean. Given its close connection with the Marines, the US Navy also became interested. The key US development was to heavy bombs capable of disabling aircraft carriers and sinking small warships. Not only could a dive bomber hit a manoeuvring target, it was a much more difficult target than a torpedo or level bomber flying a straight course. Attacks developed suddenly, and it appeared that fire-control systems designed to deal with level bombing could not cope. US Navy dive bombing was popularised in the 1931 movie ‘Hell Divers’, starring Wallace Beery and Clark Gable. The movie was named after the F8C-4 Helldiver dive bomber. The movie seems to have made a considerably greater impression on other navies than reports of US exercises.
The Douglas SBD Dauntless succeeded magnificently at Midway, sinking four Japanese aircraft carriers. It fought in all five carrier-vs-carrier battles in the Pacific, and many considered it superior to its successor, the Helldiver. It operated both as a scout (S) and as dive bomber (B). In the armed scout role it carried a 500lb bomb and extra fuel; in the dive-bomber role it carried a 1000lb bomb, as shown here. The Dauntless could also operate as an unarmed scout, with a range of 1445 miles, compared to 1300 miles with the 1000lb bomb. Although production ended in 1944, the Marines were still flying Dauntlesses in the Philippines when the war ended. Although it was small, the Dauntless did not fold its wings and thus occupied more deck or hangar space than its successor. BuAer never seriously considered adding the weight of a folding mechanism, because that would have cost too much fuel or bomb load. One weight it did add was an ASB (air to ship radar), which in turn required a new electrical system (this was in the SBD-4, which entered production in the autumn of 1942).
A 500lb bomb being loaded onto a US Navy dive bomber, January 1942. The cradle around the bomb is the crutch (trapeze) which swung it out so that it did not foul the propeller as it fell roughly parallel to the diving path of the aircraft.
A dive bomber had to carry added weight to deal with the stress of pulling out of its attack dive. That is why US and Japanese dive bombers in service in 1941–3 could not carry torpedoes (conversely, torpedo bombers could not handle the stresses of dive bombing). During the war a new generation of much more powerful engines made it possible to eliminate this distinction. The most prominent example was the British Barracuda, conceived as a dual-purpose dive and torpedo bomber, but used in practice as a dive bomber. The Japanese B7A Ryusei (‘Grace’) was analogous. The US Helldiver (SB2C) could carry a torpedo, but it was never used in combat for that purpose. Somewhat similarly, the Avenger was often used as a glide bomber, although it was not stressed for such tactics, and from time to time it disintegrated while bombing.
Generally, glide bombing (attack at a shallower angle) was practiced as a less straining alternative to dive bombing, since it still gave a better aim than level bombing. During the early part of the Second World War, the distinction between the two was not always drawn. In Norway, for example, until the Germans had airfields ashore they used long-range bombers (Ju 88s) to attack the British fleet offshore. Those aircraft often made shallow (glide-bombing) dives. British long-range barrage tactics often frustrated them. By way of contrast, the short-range Stuka (Ju 87) made true dive-bombing (near-vertical) approaches.
Aircraft structural strength limited the weight of the dive bomb, the heaviest probably being the German 1600lb armour-piercing bomb. When the Royal Navy’s Fleet Air Arm attacked the battleship Tirpitz in 1944, pilots kept their bombs on board as long as they could to ensure hits. They did not give the bombs enough altitude to accelerate enough to penetrate the ship’s protective decks. In 1941 the US Navy became interested in a solution in the form of a rocket boost, but it did not materialise. Thus dive bombing was unlikely to sink a battleship, although it might do significant damage. By manoeuvring, a diving pilot could keep his bomb pointed at a manoeuvring warship. His chance of hitting was far better than that of a level bomber. The closer the dive bomber came to a vertical dive, the closer the bomb would follow where the bomber’s nose pointed. The further from the vertical, the more important it was for the bombsight to compensate for bomb ballistics. Because it used near-vertical tactics, the US Navy relied on a simple tube gunsight. Because they attacked at a shallower angle, they required a more elaborate bombsight (development of which lagged badly in 1932–8).
The Curtiss Helldiver (SB2C) was bought ‘off the drawing board’ to replace the Dauntless in the autumn of 1940 due to the obvious threat of war. The Helldiver was designed for a 1938 competition in which the engine was the next-generation (after the Dauntless) R-2600 producing 1700hp, carrying the standard 1000lb bomb internally. The urgent order and equally urgent preparation for large-scale production made it difficult or impossible to cure defects in the design, ultimately limited strength (Helldivers sometimes disintegrated while diving, and sometimes even when sitting on a runway) and limited longitudinal stability (Helldiver dimensions were set by a requirement that two be able to ride a 41ft × 48ft carrier elevator). Modifications increased weight to the point where the Helldiver was little faster than a Dauntless, and pilots much preferred the earlier aircraft: the Helldiver was designed to operate at 11,900lbs, but at the end of 1944 it weighed 16,800lbs. Power did not increase proportionately; the later R-2600 produced 1900hp. From an attack point of view, the important advantage of the Helldiver was its large bomb bay, which made it possible to increase the bomb load as BuAer realised in 1942 that the 1000lb bomb was not enough. The bomb bay could accommodate either two 1000lb or one 1600lb AP bomb, and a special adaptor made by Curtiss made it possible to carry either a 2000lb bomb or a torpedo (which was partly external). Note that the 1600lb AP bomb did not figure in the 1944–5 attacks on the Japanese super-battleships.
Pre-Second World War exercises suggested that dive bombing would often take ships entirely by surprise. Patrolling fighters often found it difficult to follow the dive bomber into its low-altitude escape after releasing its bomb. A dive bomber was a very difficult anti-aircraft target, because its altitude was changing so rapidly. For example, a bomber diving at 300kts (which was not fast for 1941) would complete a dive from 12,000ft to bomb release in only 20 seconds. The US Navy seems to have been unique in adequately simulating dive bombers using radio-controlled targets (the British Queen Bee could not dive-bomb). Lack of realistic experience may have made the Royal Navy unduly optimistic about its ability to deal with this threat, although it was certainly aware of it. German use of dive bombers, particularly in the Mediterranean, seem to have been a terrifying surprise.
A single dive bomber was bad enough, but the tactic lent itself to multiple simultaneous attacks from different directions, because attacks were over so quickly that pilots did not have to make much allowance for the movement of their targets. Moreover, dive bombing was far more accurate than level bombing. In June 1937 the Germans tried both kinds of attack against the radio-controlled target ship Zahringen. Level bombers scored 2 per cent hits; dive bombers scored 40 per cent, and the Inspector for Naval Airmen spoke of the ‘amazing superiority of the Stuka over the ordinary bomber’.29 In 1944 a German officer commented sourly that this was true only as long as there was not a lot of anti-aircraft fire concentrated around the target, because in that case an aircraft diving straight down made an excellent target.
This Barracuda was sent to the US Navy’s test field at Patuxent River for 1944 tests. Because the Barracuda did not function well in hot, humid weather, the British Pacific Fleet was equipped with Avengers instead, even though they did not offer dive-bombing capability. (David Hobbs)
As it began to rearm in 1933–4, the Royal Navy came to realise that it could not match the numbers of carrier aircraft in the Japanese navy, which it considered its most likely enemy.