In the Imperial Japanese Army and Navy there was no alternative to visual recognition, because until early 1944 neither service used any avionics apart from communications radio and DF loops. AI radar and IFF were slow to come into Japanese service, though preliminary information on FuG 202 Lichtenstein was sent by submarine from Germany in 1942. But it would be misleading to picture Japan as a land of technology illiterates, able only to copy Western innovations. This image may have comforted the Allies until the first few days after Pearl Harbor, but it was knocked for six by the superior combat performance of the A6M (Zero) fighter, and it never had much basis in fact. In 1928 Okabe in Tokyo had been the first microwave worker to generate enough power for communications in this band of new centimetric wavelengths, and at about the same time Professor Yagi had devised the short-wave directional aerial that bears his name. Comprising a linear array of dipoles, the Yagi aerial is today seen on many millions of rooftops around the world, and it was this type of aerial that was used in the first Japanese AI installation.
Though their development was slow and often troublesome, no fewer than five types of airborne radar were worked on by the Japanese in the Second World War. At first the main effort went into ASV (air-to-surface vessel) sets, which by 1944 were operational in several types of Navy aircraft down to the familiar B5N (‘Kate’) torpedo-bomber. The three types of AI radar for night fighters were less successful. One was an Army copy of FuG 202, and though it was tested in an obsolescent Mitsubishi Ki-21 bomber in 1943 it either never reached combat units or made only an insignificant impact on operations. The much more important Army set was the E-1, operating in the S-band at near 11 cm wavelength, the main carrier of which was the Kawasaki Type 2 heavy fighter, also called Ki-45 Toryu (dragon-killer) and known to the Allies as ‘Nick’. Originally a day long-range fighter, with forward-firing guns, the Ki-45-Kai-C (modification C) version appeared in June 1944 with two 20 mm guns mounted obliquely in the mid-fuselage and, in some aircraft until October 1944, a searchlight in the nose. Gradually the AI radar was fitted and operators trained, but there is no evidence that radar played the central role in the occasional successes scored by these aircraft defending Japan against the B-29. At least the Ki-45 could reach the B-29 attack height of around 31,000 feet, and at full throttle could just overtake the speedy American bombers. Over Japan there was often chaotic radio communication, and no GCI system at all. Night fighters were thus left to their own devices, and the few successful night interceptions that took place were usually on moonlit nights when the B-29 contrails showed up from a considerable distance.
Intercepting a B-29 formation called for great courage. Whereas a Luftwaffe NJG pilot had nothing to fear from 99 per cent of the RAF heavies, the B-29 had no blind spots and carried heavy armament covering every possible direction of attack. Downwards and to the rear a fighter could be seen from three sighting stations and fired upon by six 0.5 in guns and a 20 mm cannon, and as these great bombers held tighter formation than the RAF bomber stream it was probable that, if one bomber opened fire, several others would open up on the same target. Added to the fact that head-on attacks were impractical at night, one is left with a situation in which a single fighter is faced with withering heavy-calibre fire in a stern chase at a closing speed hardly more than walking pace. A few Ki-45 night fighters attempted to get more speed and altitude by fitting only two 12.7 mm (0.5 in) oblique guns, a totally inadequate armament for the task of bringing down a B-29. Typical Ki-45-Kai-C forward-firing armament comprised a single heavy cannon of 37, 50 or 75 mm calibre, but these fired slowly and carried a very limited number of rounds. How eight of these fighters managed to bring down seven of a force of B-29s attacking northern Kyushu on the night of 15 June 1944 remains a mystery: there may have been some deliberate collisions.
The equivalent of the Ki-45 in the Imperial Navy was the Nakajima J1N1 Gekko (moonlight), called ‘Irving’ by the Allies. Planned as an escort fighter in 1940, the original J1N1-C failed to make the grade, but eventually entered service as a reconnaissance aircraft. It first operated in late 1942 in the area of New Guinea and the Solomon Islands, and though it had inadequate performance for day fighting it was locally judged to be a possible answer to the US Army heavy bombers that were making life a misery at night. The initiative to turn the J1N1-C into a night fighter stemmed from the commander of the 251st Air Corps at Rabaul, Yasuna Kozono, who proposed the same upward-firing armament as was being experimented with by the Luftwaffe. He went further, and suggested two pairs of 20 mm Type 99 Model 2 cannon, one pair firing obliquely up and the other pair obliquely down. Compared with the Luftwaffe Schräge Musik installations the inclination was less steep, a typical angle being 30°.
In March 1943 Kozono received permission for the proposed modification, and two aircraft were returned to Japan for this purpose. At the same time the Navy Bureau of Aeronautics in Tokyo recognized that the basic aircraft was eminently suitable for use as a night fighter, a category of aircraft then non-existent in the Imperial Navy. Work began on a specialized sub-type, the J1N1-S. Meanwhile the first two night-fighter conversions, designated J1N1-C-Kai, returned to Rabaul in May 1943 and soon proved their worth by shooting down two B-17s, following the next night by a B-24. This was no mean achievement, as the C-Kai had long exhaust stacks discharging above the wing, without flame dampers, and maximum speed not higher than 300 mph. At one time one of them had a trainable searchlight in the nose. They retained a crew of three, the pilot being assisted by a navigator and a gunner, the latter being needed to change ammunition drums.
These successes, the first ever gained by Japanese night fighters, were followed by others until both the original C-Kai conversions had been destroyed. But by August 1943 the definitive J1N1-S Gekko was in production, and most of the 479 of all J1N versions built were of this sub-type. The new Type 99 Model 2 guns had belt feeds, so no gunner was needed, and the previously lumpy rear fuselage was made more streamlined. From December 1944 the Gekko was the chief Navy night fighter, but its success against the B-17 and B-24 could not be repeated against the B-29; it could not climb high enough nor fly fast enough, despite the speed being increased to 315 mph at the best height of about 16,000 feet and 272 mph at 30,000 feet. In the final versions produced in 1945 a Navy-developed AI radar was fitted, again using Yagi-type aerials in a neat quadruple array and being under the control of the observer. There is no record of successful B-29 interceptions, and these aircraft either languished on the ground or were used for Kamikaze attacks.
The Army’s success with the Ki-45 led to a successor, the Ki-96, first flown in September 1943. Much more powerful, it had a speed of 373 mph and carried a 37 mm cannon and two 20 mm guns. The Army could not make up their minds whether it should have one seat or two. Eventually the Ki-96 was redesigned into the Ki-102 two-seater, flown in March 1944. One of its guns had a calibre of 57 mm, and a single shell blew an engine off a B-29 in the course of a prototype test flight with loaded guns. Only a handful of different types of Ki-102 were built, the last two being Ki-102c night fighters with two oblique 20 mm Ho-5 cannon and two forward-firing 30 mm Ho-105s. All these were new guns marking a great improvement on the old patterns used previously. The Ki-102c also carried AI radar, almost certainly E-1, and its crew comprised a pilot and radar observer. The Allied name for all Ki-102 versions was ‘Randy’.
It so happened that the best of all Japanese night fighters was a converted bomber extremely similar to the Ju 88 in character. Though many years later in conception than the German aircraft, the Yokosuka P1Y1 had precisely the same wing span, almost identical weights and engine power, a close-grouped crew of three and very similar flight performance. Like the Ju 88 it was big, tough, durable and could be flung round the sky like a single-seater. So good was it that the Navy instructed the Kawanishi company to redesign it into the P1Y1-s Kyokko (Aurora), known to the Allies as ‘Frances’. The tricky airframe was made simpler to build, the troublesome Homare engines were replaced by robust Kaseis, and the interior was rearranged with the navigator in the nose, the pilot in the centre and the rear gunner in the aft cockpit. The usual armament comprised two oblique 20 mm guns (said to be Type 99 but almost certainly Ho-5s) and a third gun of the same type in the rear cockpit for defence. Radar was fitted, related to that of the J1N1-S but derived from the widely used ASV installation with a completely different dipole aerial array, there being a single large Yagi array in the nose and an axial trio of dipoles along each side of the rear fuselage. About ninety-seven Kyokkos were built, a few having a twin 20 mm dorsal turret. It was perhaps fortunate for the Allies that protracted trials were still going on when the war ended.
There were many other ‘heavy fighter’ programmes in Japan which might have yielded a useful night defender. Among these were the Ki-46-III-Kai version of an established reconnaissance machine, with an oblique 37 mm cannon; the big Mitsubishi Ki-109 with a forward-firing 75 mm gun; the Nakajima J5N-1 Tenrai (heavenly thunder), designed to replace the J1N1-S; the Kawasaki Ki-108 with twin turbocharged engines and a pressure cabin; the Rikugun Ki-93, with two six-blade single-rotation propellers; and the Mitsubishi Ki-83, which was one of the best combat aircraft the Japanese produced in the Second World War. None of these played any part in the war, owing to a combination of muddled administration, severe technical snags, crippling shortages, and the catastrophic effect on Japanese industry of the devastating B-29 raids. Unlike the air battles in the German night sky, those over Japan – if they took place at all, which was very seldom – were one-sided. The general objective of the Japanese was not so much to develop a better fighter that would destroy the B-29 faster, as to develop one that could actually get within firing range. There was quite a difference between a Lancaster cruising at 200 mph at 22,000 feet and a B-29 cruising at 300 mph at 32,000 feet. This must be borne in mind when reflecting on the Japanese lack of success.
It so happened that the last type mentioned above, the Ki-83, bore a startling resemblance to the final US Navy night fighter of the Second World War, the Grumman F7F Tigercat. The Long Island company began its adventure into fighters twice as powerful as their contemporaries with the XF5F-1 Skyrocket flown on 1 April 1940. It continued with the Army XP-50, with nosewheel landing gear, flown on February 18 1941. This led to the XF7F-1 flown in December 1943. Powered by two 2,100 hp Double Wasps, this impressive single-seater suffered from carrier incompatibility, but went into production in April 1944 as a close-support fighter for the Marines. At the thirty-fifth aircraft, in October 1944, production abruptly switched to the F7F-2N, a two-seat night fighter with a back-seat operator for the APS-6 radar with the scanner in the tip of the nose. It had to give up the four 0.50 in guns in the nose of the -1, but still had four 20 mm cannon in the wings. The main production version was the F7F-3, with more powerful engines and built in six sub-types. The -3N night fighter was immediately distinguished by its long, knobbly nose housing the SCR-720 radar – a very different set from the little APS-6. The -4N, of which thirteen were built in 1946, was structurally strengthened and had a more streamlined nose.
It is seldom wise to predict the course of human conflict. Certainly nobody at Grumman’s Bethpage, NY, plant would have dreamed that the awesome F7F would never fire on a Jap, would spend years patrolling deep in China and would finally go into action against Koreans and America’s former allies, the Russians. Indeed, the great and – at the level of individual soldiers and pilots, genuine – alliance forged in war between the USSR and the Western Allies was to be rent asunder as soon as the fighting was over. There were deep-seated problems on both sides, but the most intractable one was the professed belief of the Soviet Union that the Capitalist nations were forever seeking to destroy it. The world became polarized into East and West; and, while the West begrudged every penny and cent spent on armaments, the East multiplied its budget for weapons over and over again. The Soviet Union was especially eager to become proficient in radar, which, apart from nuclear weapons, was the most important area of military technology in which the Communist bloc countries were seriously behind the West. During the war – called the Great Patriotic War by the Soviet Union – this had been a source of endless worry, mainly to Britain. The Soviet government had asked for ‘full information’ on every kind of radar, and in March 1942 made an explicit request for airborne RDF. This was highly secret, and not allowed at that time to fly over Europe. What fouled things up was that the Russians demonstrated that, in practice, they did not really wish to learn from their Allies. The RAF sent a large team of radio, radar and GCI experts, called ‘30 Mission’, to Moscow in April 1942. This brought mobile GCI units, VHF/RT and a lot of other equipment, and looked forward to instructing the Soviet air forces. There followed months of utter frustration, and 30 Mission repeatedly signalled to London their inability to get the Russians to use any of the equipment properly, or even show an interest. There appeared, said one signal, to be ‘bad faith’, and by early September the Director of Radar at the Air Ministry was authorized to disclose to the Soviet Union all radar information down to 50 cm wavelength (which meant many equipments used by all three services), and to invite the Russians to send a mission to London to discuss the sensitive subject of AI radar. No mission was ever sent.
I have only the British view of things, and it may be that the Russian view would be slanted very differently. But my own opinion is that the Russians were thrown off-balance by finding Britain and the United States as their Allies. They appeared to be so crippled by ideological hang-ups that they were unable to work, openly and efficiently, with the Capitalist nations to defeat their common enemy. The only exceptions were with fragments of the Capitalist nations that actually came to fight on the Eastern Front, such as the Normandie-Niemen squadron from France and 151 Wing, RAF. Had the Capitalists really wished to see the Soviet Union defeated they would not have poured such enormous quantities of armaments in through Iran and by Arctic convoys, which ran the gauntlet of U-boats and the Luftwaffe despite a lamentable failure by the Soviet naval and air forces ever to co-operate in providing protection. To the end the Russians continued, tragically, to distrust their Allies. They appeared never to understand the very real reluctance of the British to hand over their technology in AI radar to people who, going by their record, would show no interest in using it properly and would probably compromise it. Later, in 1943, a way out of the impasse was sought by asking the Soviet Union whether it would welcome a wing (two or three squadrons) of RAF Havocs to operate on the Eastern Front as detached units of the RAF under Soviet tactical command, as 151 Wing had done by day. The only problem appeared to be incompatibility of the nosewheel-equipped Havoc with soggy fields and rough wooden board airstrips, but as thousands of P-39 Airacobras, B-25 Mitchells and other versions of the Havoc (DB-7) were already in use on the Eastern Front this did not appear an insuperable difficulty. In the event the Russians did not reply, despite the fact that, had the radar-equipped squadrons been dispatched, the aircraft would undoubtedly have been given to the Russians when their crews finally returned home, as had been the case with the Hurricanes of 151 Wing.