Level Bombing
The initial alternative to torpedo attack was level bombing.24 It was the only way to deliver a bomb capable of penetrating capital-ship decks, a possibility dramatised in bombing trials conducted by the US Army Air Service in 1921. It was obvious at the time that the attacks had not been particularly realistic, since the targets had been anchored, neither shooting back nor capable of damage control. Even so, level bombing was heavily promoted between the wars by air forces as a rationale for their widespread claim that navies were obsolete.
It was widely recognised during the inter-war period that a single bomber would have a very limited chance of hitting a moving, particularly a manoeuvring, ship. A group of bombers dropping a pattern of bombs could do better. As with the torpedo bomber, level bombing required the attackers to fly a predictable course as they approached the target. The path of the bomb depended on the bomber’s course and speed and on the wind: in effect, the bomber is the gun firing the bomb, and its course and speed are equivalent to a gun barrel and to muzzle velocity. Aficionados of Second World War bomber movies will recognise this requirement, which made attacking bombers vulnerable to anti-aircraft gunfire. Conversely, it was widely understood that anything which forced level bombers to manoeuvre as they approached their targets – to jink – would ruin their aim.
Initially the RAF both in the Mediterranean and in Coastal Command in the North Sea relied heavily on light bombers like this Blenheim. It soon learned that the only effective bombing technique was very low level attack. As very few bombers were available at the time, the defence tended not to be saturated, so losses were severe. Note also the complete lack of forward-firing armament, which might have been used to suppress anti-aircraft fire. At one point Coastal Command felt compelled to revert to pre-war tactics in which aircraft attacked at much higher altitude – and tended never to hit, but at a low cost in casualties. Blenheim units rotated through Malta early in the Mediterranean war, but they were relatively ineffective. Most Axis merchant ships sunk in the Mediterranean fell victim either to submarines or to surface ships; others were destroyed in or near port by bombing or mining. Overall, mining was far more effective than direct air attack on ships at sea. (Philip Jarrett)
How long the bomber had to fly straight and level depended on how good its bombsight was; the better the sight, the less time it required for the run-in. Until the run-in, the bomber could manoeuvre fairly freely. The US Navy considered level bombing so important that its Bureau of Ordnance sponsored development of a new kind of bombsight, conceived and developed by Carl F. Norden. It was gyro-stabilised, and that in turn made it possible for the bombardier to measure, in effect, the bomber’s ground speed by tracking the target visually. Norden once remarked that the best anti-aircraft fire-control technique would be equivalent to his bombsight, operating in reverse. Just before the Second World War, the US Navy estimated that a bomber required a 45-second run-in – defenders had no more than 45 seconds to get a fire-control solution and fire their bursts. It might take as much as 20 seconds to load and fire a gun and for its projectile to reach about 15,000ft or more. On the eve of their entry into the Second World War, US Navy anti-aircraft gunners considered level bombing the most difficult threat to counter. They may have been overly impressed by the short run-in a Norden required. The US Army bought the Norden bombsight in preference to a device it had developed, and a legend grew up about its performance and the need to maintain its absolute secrecy.25
Gyro-stabilisation made the Norden equivalent to an auto-pilot, since it controlled the bomber during its final approach to the target. Wartime US Navy Avenger torpedo bombers (TBFs and TBMs) all had Norden bombsights, which were often employed as autopilots.
Level bombing from high altitude (i.e., beyond easy anti-aircraft range) proved almost entirely ineffective during the Second World War, mainly because so much uncertainty, for example concerning wind between bomber and surface, and also because of inaccuracy in tracking targets on the surface. For example, in 1940 the Royal Navy’s Force H was repeatedly attacked by formations of Italian level bombers. It found that its anti-aircraft fire did not break them up, but it did keep them too high to accomplish much. The failure of level bombing was a great wartime surprise. The only important exception seems to have been bombing by Fw 200 Condors attacking convoys, whose merchant ships were not free to manoeuvre; the Condors apparently had excellent bomb-sights.26
Skip-bombing was an alternative. It seems to have been invented before the war by the RAF, and used from about 1940 onwards. The bomber approached at low level, and it might duck and weave as it did so. The approach ended at low altitude and at extremely short range, the bomb being dropped into the water. It was intended to skip like a rock skipped across water, to hit the side of the target ship. Once the bomb was gone, the bomber pulled up, often flying over the target ship at masthead height.
From the target’s point of view, skip bombing was not too different from torpedo attack, but the attacker was flying at much higher speed and also at somewhat greater altitude. Skip bombing was brought to the US Army Air Force in 1941 by General H H ‘Hap’ Arnold, who learned about it from the British. It may have been invented independently by General George Kenney for his Fifth Air Force in the south-west Pacific in 1943, and it was used successfully against Japanese warships and merchant ships in the 1943 battle of the Bismarck Sea.27
The British ‘bouncing’ bomb was a kind of skip bomb, a rotating object intended to hit the water and skip off to hit a distant vertical object. Because it was spinning, when it hit the vertical wall, it would descend before exploding. It was developed specifically to attack German dams. By the end of the war the British had Highball, a miniature version. At the end of the war they were working up a squadron of RAF Mosquitoes to attack the Japanese fleet in Singapore from a carrier. Highball would have bounced over torpedo nets, but it would have inflicted torpedo-like underwater damage. The war ended before the attack could be mounted.
The British seem to have been unique in developing a further kind of bombing attack, featuring the ‘B’ (buoyant) bomb. This weapon would be dropped alongside a ship. Rising in the water, it would explode below the surface, creating a shockwave which in theory might break a ship’s back. ‘B’ bombs were never used in combat, and they were all ordered destroyed in 1946. The ‘B’ bomb exemplifies anti-ship weapons which, although devastating to their targets, proved entirely impractical to deliver.28
A US B-25 Mitchell climbs out after delivering a skip-bombing attack on a Japanese freighter off New Britain, 2 November 1943. (US Office of War Information wartime release)
Air-launched rockets were the ultimate strafing weapons. This is the largest one operational during the Second World War, the 11.75in US Tiny Tim (British Uncle Tom), whose warhead was a 500lb bomb. It was powered by four standard 5in rocket motors. Initial tests failed when the blast of the motor damaged the launch aircraft. Tiny Tim was used experimentally against Japanese shipping in March 1945. Franklin and Intrepid both strongly recommended production, and Intrepid aircraft successfully fired Tiny Tims during the invasion of Okinawa in April 1945. However, the Kamikaze hit on Franklin set off Tiny Tims on her hangar deck, on board bombed-up aircraft, and they added considerably to her damage.
Dive Bombing
The most important new development in anti-ship air strike warfare between the wars was dive bombing. A form of dive bombing was developed during the First World War by several countries, notably the British. Fighters or light bombers