The Germans and the Japanese seem to have become seriously interested in dive bombing at about the same time. The first dedicated German dive bomber design, the Heinkel He 50, was produced in modified form in Japan as the first Japanese naval dive bomber, the Aichi D1A1 (Type 94, hence adopted in 1934). The Germans went on to develop other types, most notably the Ju 87 Stuka. By 1941 the Imperial Japanese Navy had a high-performance monoplane dive bomber (D3A); its carrier groups included roughly equal numbers of dive and torpedo bombers.
The Royal Navy considered the arrival of German Stuka dive bombers in the Mediterranean late in 1940 a decisive factor which precluded operations in particular areas. Stukas had already shown their effectiveness at Dunkirk and in the Channel and the North Sea in 1940. The crutch under the belly could be adjusted to take either a 250kg or a 500kg bomb. Against merchant ships Stukas typically carried a 250kg bomb plus four underwing 25kg bombs; against cruisers and larger warships they used 500kg bombs (later they had a special 771kg armour-piercing bomb). Stukas typically approached a convoy from out of the sun at about 13,000ft at 150mph, releasing their bombs from about 1600ft in an 80° dive, and pulling out at about 700 to 800ft. Typically Stukas attacking large warships split up and dove simultaneously from different directions. Against destroyers a Stuka would typically approach from astern, as the pilot could more easily follow the ship’s evasive manoeuvres. That is why the Royal Navy emplaced destroyer automatic weapons, such as multiple pom-poms, so that they had wide aft arcs.
The Ju 87 ‘Stuka’ is remembered mainly for its service against land targets, but it was the most effective German air anti-ship weapon. (Philip Jarrett)
The successful 8 January 1941 Stuka attack against the armoured flight deck carrier HMS Illustrious profoundly affected the Royal Navy. Hitler had ordered Stukas to the Mediterranean in the autumn of 1940 as part of the larger plan to deploy the Afrika Korps in North Africa. His expectation was that by sinking the carrier (which they failed to do) the Stukas could tip the balance of sea power to the Italians and thus ensure successful sea support for the Afrika Korps. Although that was more than the Stukas could achieve, both the Royal Navy and Prime Minister Winston Churchill were shocked by the attack. The attack was carried out by forty-three Stukas attacking in three main waves, all approaching at 12,000ft. They checked their dives to correct aim at about 6000 to 8000ft before releasing bombs at 1500ft for the first wave and down to 800ft for later ones, which did not face such intense fire.
Most dove at 60°. At any one time about six Stukas were diving at the ship. German records showed four losses, one of them to a fighter. The fleet commander found this ‘novel’ type of attack so fascinating that he watched rather than being frightened. The Royal Navy claimed at the time that naval gunfire had brought three of them down (plus eleven probables), and that naval fighters had accounted for six more. German records showed four Stukas lost. The most important result of the March 1941 upset was the design of the ‘Battle’ class destroyers, with their all-dual purpose main batteries. This decision was reached before the destroyer massacre (by Stukas) off Crete in May 1941.
Churchill sent the Admiralty a personal minute in mid-March 1941 asking whether the Stuka had driven the Royal Navy out of the Central Mediterranean. He felt that the Admiralty had sent ships there with inadequate armament, and he wanted ships fitted with batteries of special anti-dive bomber weapons. A few days later a special meeting was convened to discuss possible countermeasures, including an apparently much-touted rocket (unrotated projectile [UP]) using a photoelectric (PE) proximity fuse. When ships first experienced dive bombing, personnel were bewildered by the spectacular nature of the attack. On the second occasion personnel were able to concentrate better, and on the third and later occasions they got the best out of their weapons. On this basis it seemed that Illustrious had fared better than most. It seemed that, given the massive scale of the attack, the worst problem was switching from one target to another quickly enough. The PE-fused rocket did not solve the problem, first because it had to be pointed properly, second because it fired too few weapons (and it might take two minutes to reload), and third because the fuze could function only under some sun conditions. Tests ashore had not taken the motion of the ship into account. At this time the LAM (Long Aerial Mine) was being developed for firing from a UP projector specifically to deal with night bombers (it took 40 seconds to establish itself). It was clearly not an anti-dive bomber weapon. The FAM, which was later widely deployed, was not a means of preventing a dive attack, because it was effective only after bomb release, but it might be an effective deterrent.
The meeting considered the pom-pom the most effective anti-dive bomber weapon; it would soon have high-velocity ammunition. Deployment of projected-wire rocket weapons was beginning. Thus 1100 ‘Pig Troughs’ (2in UP with contact fuses, four barrels) would be available by the end of April 1941, together with fifty ‘Pillar Boxes’ (20-barrel 2in UP) in June (and another 150 in July or August), plus 30 larger multiple UP mountings (twenty 3in barrels with PE fuses) by the end of May. A total of 26,000 FAM rockets were on order. Fifty Harvey projectors (PE-fused rockets) were being sent to sea for trials. There was also interest in fitting out the ex-French air target ship L’Impassible (14kts, 3in deck) with a large number of assorted UP weapons. The fleet’s existing larger-calibre UPs (Naval Wire Barrage) were not mentioned. At this time Formidable had been given seventy-five PAC outfits (rockets) mounted around her flight deck, but they do not seem to have been used in combat. Oerlikons were finally coming out of the British plant, and one proposal was to send them to the Mediterranean on an emergency basis on board long-range bombers and submarines (at this time all of them were assigned to defend merchant ships). There was also interest in a shuttle service for FAMs in the Mediterranean, ships cross-decking them when they reached port.
During the Second World War the United States developed toss-bombing, which might be thought of as an alternative way to use an aircraft to aim a bomb or other weapon (it was applied to rockets and even to torpedoes). If an aircraft releases a weapon in a climb, the weapon continues up and over. Using a computer which takes weapon ballistics into account, the aircraft can aim at a target without pointing directly at it, and thus can avoid anti-aircraft fire. The sight involved was called a bomb director, by analogy with a torpedo director.
Combined Tactics
The most effective attacks combined several different tactics, since measures to defeat one would open a ship to the others. For example, the Japanese made special efforts to co-ordinate different types of attack. The successful attack against Prince of Wales and Repulse combined high-level and torpedo bombers, both land-based. High-level bombers might not be all that effective, but they occupied channels of medium-calibre fire which might otherwise have been devoted to torpedo bombers. Japanese tactics reported in mid-1943 employed level bombing preceding torpedo and dive bombing attacks mainly as a distraction.32 On the other hand, the Japanese did not attack from different directors to overwhelm the defenders, because each individual aircraft had a relatively limited chance of hitting its target. Concentrating an attack gave the best chance of making some hits.
By 1943 the Japanese were also sometimes glide bombing at a 45° angle, beginning at about 12,000ft and releasing the bombs in level flight at 2500 or 3000ft. In ‘swing’ bombing, an aircraft flew towards the target until it reached the perimeter of anti-aircraft fire, then entered a banked turn and released a bomb which centrifugal force threw towards the target – a kind of toss-bombing. At this time the Japanese had not yet tried low-level anti-ship attacks, although they had certainly experienced such tactics.
Torpedo bombers generally approached at high altitude (to spot their targets at maximum range), reducing altitude and forming a loose string or wedge or diamond formation while still out of range. They attacked in multiples of three, most frequently nine aircraft. Dropping range was typically 1000–1500