The Mitsubishi Ki-21 twin-engine bomber (the Americans gave it its name "Sally") became a landmark for the Japanese Air Force. Production of this aircraft began at the very beginning of 1938. According to flight performance, he stood on a par with the most successful and advanced machines of his time. Despite the relatively low bomb load (from 750 kg to 1 ton), the average Ki-21 bomber was produced until the fall of 1944. In total, more than 2060 aircraft were manufactured. The Ki-49 who replaced him did not manage to take the place of his predecessor. In the japanese army aviation The Ki-21 was in service much longer than any other machine. The fact that the Ki-21 was used in a desperate operation on May 24, 1945 during the battles for Okinawa is widely known. Nine Ki-21-II without weapons, but with a dozen paratroopers on board tried to land at Yentan airfield.
It was the absence of a worthy replacement, which ensured the long life of this bomber, which led to the fact that by the year of 1943, army bombers were in the most inauspicious position among the Japanese air forces. If the fighter regiments (Zentaks of Centai) received in a small amount the new X-61 “Hien” type vehicles, then the Ki-21 and Ki-49 aircraft remained in service with the bomber “Sentai”.
The main types of army aviation bombers developed in the skies of China, which had been well-established in the skies of China before the war, quickly grew old and could not be expected in the near future. Such a deplorable state of affairs on the eve of the decisive battles in the Pacific Ocean was explained not by the miscalculations of the army air headquarters (Koku Hombu), but strangely enough, the very logic of the development of the army bomber aircraft of Japan.
Up to the entry of Japan into the Second World War in Western countries, it was considered that only the outdated copies of foreign aircraft were in service with its air force. And even the appearance of quite modern types of machines in the sky of China at first passed unnoticed by western experts. This conventional wisdom was valid only until the early thirties, when Japanese military and naval aviation decided to put an end to foreign dependence in replenishing the aircraft fleet.
February 15 The 1936 Army Army Headquarters prepared requirements for a number of aircraft that meet the current level of aviation development. Given the military-political situation in the Far East, the Japanese General Staff considered the Soviet Union as its main opponent. The Japanese did not believe in the possibility of a protracted war with China. By unleashing a second Sino-Japanese conflict, the Japanese General Staff assured the emperor that the “problems” would be resolved in literally three to four months. But with the capture of vast Chinese territories, the boundaries of a possible theater of military operations against the Soviet Union dramatically expanded. The inability of the Japanese army aviation to maintain superiority in the sky and to ensure the advance of its armies deep into the territory of a “potential enemy” became completely understandable. This issue was given serious attention, and the creation of a new bomber was considered a necessary condition.
Specifications for the new "heavy" (according to the Japanese classification) bomber asked the speed of the order of 400 km / h and the range to 1500 km. The aircraft was reported to reach altitude in 3000 no more than in 8 minutes. All these requirements at that time were considered to be quite high. Only armament was weak: three 7,62-mm machine guns and 750 kg of normal bomb load. The possibility of using a bomber in the conditions of the Siberian frosts was especially stipulated.
According to this assignment, three major aviation firms in Japan prepared their projects: Kawasaki presented Ki-22, Nakajima - Ki-19, and Mitsubishi - Ki-21. It was decided to build prototypes for the last two projects. Experienced Mitsubishi Ki-21 made the first take-off of December 18 of the year 1936. Both competitors turned out very similar and had similar sizes. Ki-19 showed on tests in Tachikawa higher bombing accuracy and excellent controllability. And the Ki-21 had a lower wing load and had better flight performance.
The customer could not choose the best aircraft. We decided to repeat the test after the elimination of the revealed observations. The designers Ozawa and Nakata from the Mitsubishi firm managed to do it better. While modifying their Ki-21, they used a number of competitor solutions. For example, following the model of the Ki-19, a new bow was completed, which the navigators liked so much. On the Ki-21, the upper turret was also replaced with an elongated blister, and the ledge under the fuselage was removed. These improvements have improved the stability of the bomber when dropping bombs.
In addition, at the request of the military Mitsubishi X-5 825 HP motors. replaced by competitor engines - Nakajima Ha-6 850 horsepower The customer was finally satisfied, and Ki-21 was announced the winner. In November 1937, the army entered into a contract for serial production to Mitsubishi. The new aircraft was given the designation "type 97" - "heavy bomber army type 97 model 1" (Ki-21-Ia).
The bomb compartment was under the spar of the center section, above them were two gas tanks, pressed to the left side, on the right side was arranged a passage in the tail of the aircraft. The first and second pilot (acting navigator) were placed nearby, the scorer was sitting in the nose of the plane, the gunner-radio operator - in the tail section.
Defensive armament consisted of three 7,7-mm machine gun "type 89". One - in the nose lens installation at the disposal of the scorer, the second - in the upper elongated blister, and the third - in the lower hatch.
While the Ki-21 and Ki-19 tests were underway, a war broke out in China. At the very beginning of the conflict, it turned out that the Japanese Army Air Force did not actually have a bomber that could hit targets deep in enemy territory. As a result, the tasks of army aviation were at first more than modest - providing air defense to occupied Manchuria, and the main burden of the conflict fell on long-range bombers fleet Mitsubishi G3M.
In order to rectify this state of affairs, in addition to the urgent deployment of the Ki-21 production at two factories at once, the bomber decided to buy abroad. The choice fell on the Italian "Fiat" B.R.20. The company Aeritali, which created it, with amazing speed, fulfilled the order for 85 airplanes, which came into service with two bomber "sentes" of Japanese aviation. The deliveries of the serial Ki-21 began from the factory in Nagoya in May, 1938, and from the factory in Ota - in August. Already in December, 1938-th “sentai” was organized on the basis of Ki-21 on the basis of Ki-60, which was baptized in the last days of the year.
All three “heavy” bombers with Ki-21 and B.R.20 were used extensively in the winter of 1939 for strikes on major cities in China.
The Chinese air force, faced with the overwhelming domination of the Japanese in the air, resorted to a very peculiar tactic - they took their aviation units beyond the range of the Japanese fighters, meeting the Japanese bombers without a fighter escort. In such circumstances, the aggressors often fell into this "meat grinder". Sometimes, whole units did not return from battle. It was especially hard for the “Italian” - in less than three months both “Sentai” with B.R. 20 practically lost their combat capability. The Ki-21 proved to be somewhat better - it affected a long range (while B. R. 20 often acted at the limit of its range), as well as the higher survivability of the Japanese bomber. However, among them the losses were very noticeable.
In May, the 1939-th conflict broke out on the Khalkhin-Gol River, and there they urgently transferred twelve Ki-21 and B.R.20 to each. Here their combat debut was the last successful operation of the Japanese against the Soviet air force - a massive raid on the airfields of June 27. However, in this raid over the Tamtsak-Bulak airfield two Ki-21 were shot down. In total, six such machines were lost during the conflict. The fighting over Mongolia and China clearly showed the weakness of the defensive armament Ki-21, and they decided to urgently strengthen it. Already at the end of the summer, 1939-th went into a series of modification Ki-21-Ib. A fourth 7,62-mm machine gun was fixed on it in the tail section.
Gas tanks partially protektirovali rubber and introduced elements of the crew’s body armor. Soon, a modification of the Ki-21-Ib appeared. On it, another machine gun was installed in the side window of the navigator's cabin - right behind the pilots' seats, and they also provided a suspension in the bomb bay of an additional fuel tank.
It must be said that the Japanese air force headquarters adhered to a rather pragmatic rule: after setting up a new aircraft in a series, the task for the next aircraft of the same class was immediately issued. Ki-21 has just completed the tests, and Nakajima has already been assigned a task for the future bomber Ki-49, which was to replace the Mitsubishi aircraft.
Based on the outcome of the fighting in China, a new bomber was demanded to ensure the possibility of action without cover by fighters due to the achievement of high-speed aircraft and equipping it with solid defensive armament. It was necessary to ensure the speed of the order of 500 km / h, which was 15% higher than that of the Ki-21. In this case, the flight range was set equal to 3000 km, and the combat load - 1000 kg. The crew of the aircraft required to protect the armor, and make the fuel tanks protected.
The assignment for the new bomber was sent to the Nakajima company, which provided its best specialists for the design work. Engineer Koyamu was appointed in charge of the project. The development of the new bomber began in July 1938.
When the army gave preference to the Ki-21 a year ago, Nakajima’s employees were able to study the technical characteristics of a competitor in the competition, so now they knew the car they needed to beat. During the development of the bomber great attention was paid to ensuring good handling. For this purpose, a medium plan with a wing of relatively small elongation was chosen, which made it possible to obtain good handling and high maneuverability at medium and low altitudes. The chord of the center section was made longer than the console chord at the engine nacelle, which ensured the placement of six protected fuel tanks in the center section, reduced the overall air resistance, and also allowed the flaps to be installed behind the engine nacelles.
Defensive armament included a 20-mm cannon in the upper turret and on the 7,7-mm machine gun "type 89" in the bow, bottom and side installations. A similar machine gun was installed in the tail turret, it was the first installation of this kind on the aircraft of the Japanese Army Aviation. The large bomb bay was almost equal in length to the center section.
The first prototype took to the air in August 1939. She was equipped with two Nakajima XA-5 KAI radial air-cooled motors, with take-off power in the 950 hp. and 1082 hp at a height of 4000 m. This bomber was favorably received by combatant pilots, who noted good maneuverability and controllability. The following two prototypes were equipped with design 1250-powerful Nak-Jima X-41 motors. They were made at the end of 1939 of the year. The next seven prototypes produced next year differed only in the installation of new automatic propellers. All prototypes have undergone quite lengthy comprehensive tests, revealing the need for only minor modifications in the field of body armor and crew accommodation. In mid-March 1941, the new aircraft was adopted and assigned the name - “Army-type heavy bomber 100 model 1” (Ki-49-I) “Donry” (storm dragon).
During the period of the Ki-49 tests, the message about serious losses of the Ki-21 bombers, especially without fighter cover, came again from China. The reaction to this was the creation of an Nakjima Matsumura engineer based on the Ki-49 long-range fighter Ki-58. From the end of 1940 to March, 1941-th produced three prototype fighters for the Nakajima X-109 motors. Instead of a bomb bay, they were fixed on a gondola, they increased the crew’s protection, the armament consisted of five 20-mm quick-fire guns Ho-1 and two 12,7-mm machine guns Ho-103. It was planned that such fighters would cover the connections of the Ki-49 from the flanks; however, with the advent of the Ki-43 “Hayabusa” fighter, the problem was solved by itself.
While the tests of the Ki-49 were under way, the Air Force headquarters requested the continuation of work on the modernization of the Ki-21, in order to increase speed and altitude characteristics. Moreover, it was planned to do this without stopping the main assembly lines - the war was approaching. Engines "type 97" had to change the new 14-cylinder Mitsubishi Ha-101 takeoff power to 1500 hp. These motors with screws of increased diameter were mounted on the first production model of the Ki-21-Ic, which became the prototype of the new Ki-21-II.
Flight tests began in the spring of the year 1940. The results were encouraging - the speed increased to 478 km / h at an altitude of 4500 m, the car climbed to an altitude of 6000 m in 13,2 minutes, and the practical ceiling reached 10 000 m. The company immediately received instructions from the air headquarters to deliver Ki-21-IIa (“ Heavy bomber 97 type army model 2А ”) in a series at the Nagoya plant.
The production of the Ki-21-II gained momentum during the winter of the 1941 year, and most of the units had time to get a new model before the outbreak of war with the United States.
According to the combat plan, the 3-i Hiko Sidan (Air Division) was supposed to support the fighting in Malaya and Burma. It consisted of "Sentai" №№ 12, 60 and 92. But the air division did not have time to completely redeploy to Indochina. The planning of hostilities in the southern direction was for the army headquarters a complete surprise - its main adversary, especially after Khalkhin Gol, was considered by the USSR. As a result, army aviation crews and their aircraft turned out to be practically unprepared for combat work on the waters of the Pacific Ocean. Again, just like four years ago in China, fleet aviation assumed the main tasks, while army aviation had to operate only over the continent and large islands.
The fighting began for Japan in very difficult conditions, there was an acute shortage of spare parts due to its remoteness from the metropolis and difficulties with delivery. In addition, on the eve of the war, the main base of the 3 Division, the airfield in Phnom Penh, was out of action from heavy rains. But despite this, one of the units, which was based in Saigon, was able to very successfully support the landing of troops in Kota Bharu.
Over the next two months, the crews of the X-21 3 division actively supported the offensive of the ground forces, taking advantage of the lack of air resistance. But 14 “Sentayu” 4 “Hiko Sidan”, who fought in the Philippines, and then in Burma, was not lucky. In Burma, the 14s and 62s of the “Sentai” attacked the Rangoon airfield of Taungo, where the Japanese planes met quite a strong opposition from the American Kittyhawks and Buffalo from the British Air Force 67. During these battles, the 14 th "sentai" lost most of their aircraft. As a result, again the question arose of further improving the defenses of the bomber.
The main drawback was the limited firing angles from the top machine gun installation. As a result, the upper blister of the shooter was removed, installing a large conical turret with a large-caliber machine gun "type 1". The tower had a foot pedal drive.
Deliveries of the Ki-49 bomber, which was planned to replace the Ki-21-II, began in the late summer of 1941. The first on the new Ki-49 was the 61 th “sentai”, which previously flew the Ki-21. But due to the slow pace of delivery of “Donry” to the troops, the transition of this “sentai” to new cars was delayed until February of the 1942 year. Soon, the combat debut of the aircraft took place in the skies of China, after which Ki-49 actively participated in the battles over New Britain, New Guinea, and even over Northern Australia.
During the battles, it turned out that the power of the Ki-49 engines was clearly not enough, because of this, the machine’s controllability suffered. The speed of the new aircraft - its main advantage over the bomber Ki-21 - no longer allowed to move away from the new enemy fighters. In addition, the bomb load was even lower than that of its predecessor. The pilots positively evaluated only armor protection, solid small arms and the absence of "dead", non-fireable defensive weapons, sectors.
In April, it was decided to install 1942 on Ki-49 Nakajima XenumX 109 motors with a capacity of 1450 l, p. This required only a slight change in the engine nacelle, since the new engine was slightly different in size from its predecessor. But the oil radiator, previously standing inside the hood, had to be placed outside under the engine nacelles. Other improvements were made according to the experience of the battles: armor protection and tank retrofitting was improved, a new bomb-aim was installed, while the weapons remained, as in the previous modification. A new version of "Donry" went into the series under the name Ki-49-IIa. Deliveries of this modification began at the end of August 1942. Combat experience also revealed that machine guns of rifle caliber are ineffective against Anglo-American fighters. Therefore, they were all replaced by large-caliber "type 1" (Ho-103). The new version was named Ki-49-IIb.
The Ki-49-II was never completely able to be replaced in the military units of the Ki-21-II, and was mainly used in New Guinea and in China. By the time of the American landing on the island of Mindoro, the few remaining aircraft were used by kamikaze pilots to fight the Allied ships. Despite the fact that before the appearance of the Ki-67, the bomber stood out with good armor and powerful enough weaponry, the Ki-49 still could not satisfy the air headquarters. The speed characteristics at low and medium altitudes were insufficient, and the handling was worse than that of the Ki-21-II.
To enhance the performance of "Donru", on Nakajima decided to use the most powerful of the existing engines XA-117 in 2420 HP. At the same time, the engine power was planned to be brought to 2800 hp, but the engine was hardly completed, and as a result, only six Ki-1943-III were built with these engines until the end of 49.
The result of serial production was 819 Ki-49, of which 129 Ki-49-I and 667 Ki-49-II. Despite all its shortcomings, Ki-49 was actively used for a variety of special tasks. So, magnetometers were installed on the Ki-49-I to search for submarines, some of the Ki-49-II were used as landing aircraft. Others were converted into parts in night fighters. At the same time, a searchlight was mounted on one aircraft, and the 75-mm cannon was mounted on the second one. When used as a kamikaze aircraft, weapons were dismantled from a bomber, the crew was reduced to two pilots, but the bomb load increased to 1600 kg.
Donry's combat career was not bright and long. And he is known in stories Japanese aviation only as the first combat aircraft equipped with a tail turret. Paradoxically, Ki-21 was destined to outlive its "heir." The plant in Nagoya continued to produce Ki-21-II until September 1944. Only after the start of serial production of the Mitsubishi Ki-67 bomber "Hiryu" began to withdraw Ki-21 from combat units. At the same time, in service with the 58 th "sentai" Ki-21 remained until the very end of the war.
The Ki-21 aircraft was produced for seven years and took part in almost all operations of the Japanese Army Aviation. By the time it was put into service in 1938, it was an outstanding bomber, but over time more sophisticated aircraft began to appear in Japan’s opponents, and the Ki-21 was hopelessly outdated. Still, this Japanese bomber served in the Japanese Air Force longer than any other aircraft. Ki-21 continued his service when his "peers" - the American "Martin-139" and the Soviet Security Council - had long been "gone from the scene."
Firsov A. Mitsubishi Ki-21 // Aviation Collection No. 4. Part of 2. 1996. C. 27-31.
Firsov A. Nakajima Ki-49 // Aviation Collection No. 4. Part of 3. 1996. C. 12-15.
Doroshkevich O. Aircraft of Japan of the Second World War. Minsk: Harvest, 2004. C. 56-59, 82-85.
A. Firsov. Two samurai swords // Wings of the Motherland. 1995. No.6. C. 22-25.
Bakursky V. Novikov M. Japanese Aircraft // Aviation and Cosmonautics. 1994. No.1. C. 11-24.