carrier air defence: if the Japanese fleet could outreach the US fleet, and if its aircraft could penetrate US defences, then it could strike without being struck. The Japanese consistently managed to outrange the US fleet, but the combination of effective fighter control and effective anti-aircraft fire made that outreach useless. The Ryusei was intended to replace both the standard attack aircraft: the B6N torpedo bomber and the D4Y dive bomber. Given enough engine power, an airframe stressed to dive-bomb could lift a torpedo. That was the case with both the US SB2C Helldiver (although it was not used as a torpedo bomber) and the British Barracuda (a torpedo bomber used exclusively as a dive bomber). Manoeuvrability was to be equal to that of a Zero (A6M) fighter, to give the Ryusei reasonable immunity from interception. Normal range was to be 1000nm (maximum 1800nm). The prototype was completed in May 1942. Note that the operational concept considerably predated Midway. Production seems to have been hampered by slow engine development, as it did not begin until April 1944. (Philip Jarrett)
As the US fleet came closer to Japanese land bases, night torpedo attacks became more common, using shore-based single-engined aircraft. Typically a reconnaissance aircraft spotted the fleet at dusk and provided a rough location to the strike force. Night tactics employed off Palau in the spring of 1944 were considered typical. Enemy aircraft milled around outside gun range, then formed up for a sudden run in at low altitude (200–300ft) and medium speed (150–180kts), low altitude having been chosen to avoid US radar. They approached in a rough line abreast. During each such attack a single aircraft stood off about 20–30nm away, probably co-ordinating the attack.
Maximum strike range from base was about 150nm.23 This distance was probably related to the uncertainty of future target position due to the time interval between report and attack. The strike force spread out into a wide arc once it got to within 15–20nm of the fleet. ‘Betty’ and ‘Jill’ both carried what the British called Air to Surface Vessel (ASV) radar, which was equivalent to the early-war British metric-wavelength set using dipole antennas along the body of the aircraft. It could not look dead ahead. At any height above 1000ft it could detect a battleship at a range of 45nm. It appeared that the strike force spread out either because homing on search radars became confused (the fleet had so many of them) or because ASV was inaccurate looking right ahead. The attack then spread out, aircraft dropping to 500ft and forming smaller attack groups.
The standard British Monoplane Air Tail, under a Beaufort. (Dr Raymond Cheung)
An Italian torpedo with air tail, under an SM 79.
Japanese doctrine was to place the target between the striking force and the moon (the preferred time was when the moon was between 10° and 50° above the horizon). The target was illuminated either by the shadowing aircraft calling in the strike or by two specially-assigned strike aircraft. In either case the shadowing aircraft dropped course lights behind the target when the strike force was about 20nm away. As soon as they could be seen by the strike force, it altered course to line up with these flares. When in the desired position, the strike force gave the signal to illuminate, at which time flares were dropped on the side of the target away from the strike force.
Strike forces could vary from three to as many as forty aircraft; by late 1944 carrier strikes on Japanese airfields were limiting typical numbers to no more than twenty night torpedo bombers. Aircraft flew most of the way to the target at 3000–4000ft, and sometimes not more than 1000ft, which would limit long-range radar detection. New Japanese tactics (as of late 1944) included a higher approach so that the attackers could use their own radar effectively. Striking forces sometimes homed on US air-search radars.
The Italians developed Motobomba, a circling electric torpedo which could be dropped in the path of a moving force. In that way it functioned as a cross between a torpedo and a mine, since it covered a larger area than a mine but did not have to be aimed like a torpedo. Motobomba was adopted by the Germans in the Mediterranean. (Dr Raymond Cheung)
By 1944 the Japanese were well aware of ‘Window’ (chaff: strips of aluminium foil or other radar reflectors), which had been used against their German allies the previous year. During the invasion of Saipan (June 1944), Japanese attackers made frequent and varying use of it, in US eyes demonstrating a good understanding of its potential. Often a group of aircraft dropped ‘Window’ while orbiting, then left the infected area to attack from a different direction. It was intended to leave US radar operators uncertain of whether there were still enemy aircraft in the infected area, hence unwilling to concentrate defending fighters on the new attack. At other times raiders attacked from the infected area. It was difficult to detect Japanese aircraft until they were about 5nm closer than the near edge of the ‘Window’ zone. The Japanese also began to exploit US IFF (Identify Friend or Foe). In this way a group of Japanese aircraft were able to approach 7th Fleet units on 6 November 1944 near Leyte and inflict damage.
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
