Nakajima's Demon: The Ki-44 Shoki

Throughout World War 2 the standard practice of all of the major powers both Allied and Axis in introducing a new combat aircraft into operational use was that use in combat followed an extensive flight test and pre-production development period. One of rare exceptions to this established practice came with the Nakajima Ki-44 which was christened "Shoki" (Demon) by its pilots. And it wasn't on account of its performance against Allied aircraft- the first pilots to fly the Shoki in combat gave it that name out of disdain for an aircraft that represented a new philosophy in fighter aircraft for the Imperial Japanese Army Air Force.

The Nakajima Ki-44 Shoki's Allied code name was "Tojo"
(San Diego Air and Space Museum Collection)

Until the Ki-44 Shoki (codenamed "Tojo" by the Allies) came along, the prevailing wisdom in Japanese fighter aircraft design was to put maneuverability as the prime design objective- all other considerations were secondary, which to quite an extent explained the relative lack of significant armor protection for fighter pilots, as that would have added weight to the aircraft and adversely impacted maneuverability.

Nakajima had been exploring the ideas of trading off maneuverability for increased speed as far back as the mid-1930s after the experience of the brief border war with the Soviets in which the Polikarpov I-16 savaged the IJAAF by using its superior speed and diving abilities to avoid close combat with the more maneuverable Japanese fighters and conduct hit-and-run attacks. Based on the experience, Nakajima's engineers contracted the services of two French engineers from the Dewointine aircraft company to develop the Ki-12 experimental fighter that in 1935 was more modern and faster than anything else the IJAAF was fielding but it remained experimental as it was deemed too radical for the established fighter design philosophy of the day.

The lead engineer at Nakajima just prior to the outbreak of the Second World War was Professor Hideo Itokawa (who later would become the father of the post-war Japanese space program and have an asteroid named for him in honor of his contributions to space science) revisited the ideas behind the Ki-12 experimental fighter by using a short-span wing which would make for a faster fighter that if highly-loaded, could also be a stable gun platform at high speed. His work is what resulted in the Ki-44 Shoki- a powerful radial engine but a comparatively stubby wing with much higher wing loading that other Japanese fighters.

By 1940 there was a greater willingness in the IJAAF for new ideas and it was decided by the Japanese High Command that the Ki-44 Shoki prototypes would be combat tested before going into production. On 15 September 1941 the IJAAF created an evaluation squadron called the 47th Dokuritsu Hiko Chutai (Independent Air Squadron) equipped with the seven prototype Shoki fighters that were quite literally handbuilt by Nakajima. The initial plans were to combat test the Shoki prototypes in China, but with Japan's declaration of war in December on the Allies, the so-called "Kingfisher" Chutai and its seven prototypes were sent to Malaya for use against the British. The Shokis ranged across the peninsula as the invading Japanese forces pushed the British southward to Singapore, scoring victory after victory on hapless British fighters.

By early 1942, Nakajima began work on 40 pre-production Shokis which had improved armament and other modifications such as a combat flap that was a modified Fowler flap that could be extended rearward with little deflection to improve the lift from the Shoki's stubby wings. As production kinks were being worked out, the Doolittle Raid in May 1942 laid bare the vulnerability to the home islands to Allied air attack and the 47th Chutai was recalled from Malaya for home defense duties where its speed and rate of climb made it a natural bomber interceptor. The last pre-production Ki-44 Shoki was delivered in October 1942 and by the end of 1942, the Imperial Japanese Army Air Force formally accepted the Shoki for operational use- after the prototypes had been in combat for nearly a year!

The Shoki's performance led it to be used primarily in the defense of the Home Islands
(Hasegawa)

In the fall of 1944 the last of the 1,225 Ki-44 Shoki fighters was delivered to a home defense unit. By that point in the war, the Shoki was used primarily with reasonable success against the B-29 Superfortresses that were ranging all across the home islands. After the war, the Nationalist Chinese operated the Shoki against the Communists, who themselves had their own Shoki squadrons which were flown by Japanese mercenary pilots. The last Shokis used by the People's Liberation Army Air Force were retired in the early 1950s. No Shokis survived to this day, but a college in Xian, China, has a wing center section. 

Further reading:

The Mitsubishi J8M Shusui: The Tragic History of the Japanese Komet Fighter

The Coming Kamikaze Threat in World War II We Never Faced

Master Sgt. Red Erwin, One of Many Heroes

The Ad Hoc Lashup That Resulted in Japan's Best Fighter of World War II

Source: Air Enthusiast, Volume 3, Number 1 (July 1972), "Nakajima Demonology: The Story of the Shoki" by William Green, managing editor, Gordon Swanborough, editor. Pilot Press Ltd, 1972, p17-25.

The Coming Kamikaze Threat in World War II We Never Faced

The USS Callaghan, the last Allied ship sunk by kamikazes.

As the American fleet began to become proficient at meeting the kamikaze threat during the Second World War, night time was usually a period when sailors got a respite from the waves of suicide attackers- the vast majority of kamikaze attacks that took place were during the daylight hours. At night the fleet could repair damage from the day's attacks, sailors could get some rest, and ammunition and supplies for the next day's battles could be stocked. By the time of the invasion of Okinawa in April 1945, the Japanese were already in full swing preparing the Home Islands for the anticipated Allied invasion. Operation Olympic was the code name for the invasion of the southernmost of the Home Islands, Kyushu, and it was scheduled for November 1945. The size of the invasion fleet would dwarf not only what was used at Okinawa, but it would also dwarf the Allied landings at Normandy on D-Day in 1944. Approximately just over 2,700 ships and landing craft participated at Normandy; the invasion of Kyushu would have required over 4,000 ships. In twelve days, over 300,000 American troops came ashore at Normandy; on the beaches of Kyushu during Operation Olympic, it was planned that the same number of American troops would storm ashore in just the first *three* days. Therefore in Japanese defense planning for the defense of Kyushu, called "Ketsu-Go", kamikazes were a key part of disrupting the Pacific Fleet Amphibious Force/Task Force 51. Little known to most, though, is that the planned kamikaze threat would have been of a level of ferocity and technique not widely faced by the US Navy in the Pacific War. 

Through most of the war, the kamikaze threat consisted of primarily front-line aircraft. However, the submarine blockade of Japan made getting strategic materials like the ores used in metal increasingly difficult. Bauxite, for example, is an ore that is the main source of aluminum and the Japanese aircraft industry's main source for bauxite were open pit mines near Singapore. As early as 1943 thoughts began to shift towards the use of wood in new aircraft designs and the Germans had even provided the Japanese with plans for the De Havilland Mosquito, the Royal Air Force's "Wooden Wonder". Mosquito components that had been captured were even shipped to Japan aboard the Imperial Japanese Navy submarine I-29, but it was sunk in July 1944 near Japan. While the Japanese were aware of wood's natural radar defeating properties, any consideration at this point in using wood in aircraft designs was more a practical matter with the ore shortages; any benefits against Allied radars was seen rather remarkably as a secondary and less important benefit. 

Yokosuka K4Y1, probably the type that sank the Callaghan.

By the time the Battle of Okinawa was winding down, "Ketsu-Go" was in full swing on Kyushu and a key part of the defense was the use of massed kamikaze attacks. But the state of Japanese aircraft industry was in disarray with the B-29 attacks and the ongoing ore shortages. In July 1945 to meet the required numbers of kamikaze aircraft, all of the training units were converted to kamikaze units which added thousands of experienced pilots but over 5,000 antiquated biplane trainers made of wood and fabric. But again, at this point in the war, no one in Japan had realized that an elderly biplane trainer was a lot harder to spot on radar- plans at that point were to offset the slow performance of the biplane aircraft by shifting the kamikaze attacks to the night time, the traditional sanctuary period for the American fleet. However, somewhere in the Japanese command structure connected all the dots- on the night of 28 July 1945, the Fletcher-class destroyer USS Callaghan was on radar picket duty off the coast of Okinawa. In a time before the advent of airborne early warning aircraft, radar picket destroyers patrolled the edges of the fleet to search for inbound kamikazes. On this night, an elderly biplane floatplane, most likely a Yokosuka K4Y1 trainer, was warded off on its first pass, but it came around undetected for a second pass and struck the destroyer, sinking it with the loss of 47 sailors. The following night, another elderly biplane struck another radar picket, the USS Cassin Young- though not sunk, 22 sailors were killed and the ship had to withdraw from action for repairs. A third destroyer, the USS Prichett, was aiding the stricken Callaghan, was very nearly sunk by another elderly biplane on a kamikaze mission.

Yokosuka K5Y biplane trainer.

The destroyers had difficulty on downing the attackers for three reasons- it was night, not the usual time kamikazes attacked, secondly, the wood and fabric biplanes were difficult to spot and track on radar, and lastly the wood and fabric construction threw off the proximity fuses of the anti-aircraft guns- the proximity fuse's sensor that triggered the detonation of the round was optimized for metal aircraft; against the old wood and fabric biplanes, the proximity fuzes detonated the round too late, or in some cases, not at all. The action that night against those three radar picket destroyers changed thinking on the role of the 5,000+ elderly biplane aircraft that were going to be used as kamikazes for "Ketsu-Go". Here was an unexpected weapon that could counter the American technological advantages in radar and proximity-fuzed shells fired by anti-aircraft guns. American intelligence analysts had seen the massive change in the air forces of Japan in the summer of 1945 and were well aware of Japanese interests in wood, but it hadn't occurred to the Navy that this was a possibly game-changing combination that would have threatened initial phases of Operation Olympic. It was assumed that fuel shortages would keep most Japanese aircraft grounded and this misconception was reinforced by the increasing lack of air action against the B-29 raids and that US warships even managed to get close enough to the Home Islands to shell coastal targets without getting attacked. In fact, the Japanese had stockpiled fuel just for the use of the kamikazes in "Ketsu-Go". 

Tachikawa Ki-17 trainer aircraft.

At Okinawa, only one of the US Navy's carrier air wings was trained and equipped for night combat, that being Night Air Group 90 embarked aboard the USS Enterprise. By November 1945, only one additional night air group would be available for Operation Olympic, giving only 50 aircraft to defend the invasion fleet at night against well over 5,000 night kamikazes that would have been difficult to spot on radar, using the mountainous terrain of Kyushu to mask their approaches to the invasion fleet, and be of a construction that would probably render a large portion of the proximity-fuzed shells ineffective. 

It is perhaps a blessing that the Japanese surrender following the atomic bombings of Hiroshima and Nagasaki took place. The kamikaze plans for "Ketsu-Go" alone would have well resulted in significant casualties on the shores of Kyushu, but instead history is left with the USS Callaghan as the last Allied ship to be sunk by kamikazes- and that night on 28 July was a small preview of the storm facing the US fleet in the waters of the Home Islands.

Source: Hell to Pay- Operation Downfall and the Invasion of Japan, 1945-1947 by D.M. Giangreco. Naval Institute Press, 2009, p125-137. Photos: Wikipedia.

The Ad Hoc Lashup That Resulted in Japan's Best Fighter of WW2

Japan's finest fighter of World War 2.

Unlike Germany and the Allies during the Second World War, the vast majority of Japanese fighter aircraft were powered by radial engines while other nations had a mix of both radial and inline engines for their fighter units. Only one production-standard Japanese fighter entered service with an inline engine, the Kawasaki Ki-61 "Hien" (Allied code name Tony). Over 2,500 Ki-61s were produced and saw service with the Imperial Japanese Army Air Force (IJAAF) from 1943 to the end of hostilities in 1945. The Hien was designed by Kawasaki's chief designer, Takeo Doi and his deputy, Shin Owada (Doi would later go on to design the postwar YS-11 airliner) in response to an IJAAF requirement for a multirole fighter that would use a license-produced version of the German Daimler-Benz DB601 liquid-cooled inline engine that also powered the Messerschmitt Bf 109. Proving itself to be a promising design, the Ki-61 turned out to have a major Achilles heel in its Kawasaki-built engine which was designated the Ha-140. Though the DB601 would be one of the Second World War's finest engines, by the time the Ki-61 entered service it was an old design that was already being outclassed by more powerful engines of both radial and inline design. Worse yet, the DB601 had very tight manufacturing tolerances and in Japanese license production, getting Ha-140 engines built as well as the DB601 proved elusive given the increasing toll being taken on Japanese industry which found itself constantly short of quality metals and lubricants given the tightening US Navy submarine blockade of the home islands. 

Ki-61 to Ki-100.

Worse would come as the war progressed into 1944 with Kawasaki's Akashi factory constantly being plagued by supplier shortages and properly manufactured crankcases and cylinder blocks. By the spring of 1944, more than half of the Ha-140 engines produced at Akashi that did leave the assembly line failed to pass acceptance testing! As a result, at Kawasaki's facility in Kagamigahara that produced the Ki-61 fighter found itself with increasing numbers of finished fighters sitting in open storage waiting for their Ha-140 engines. Matters worsened on 19 January 1945 when B-29 Superfortresses completely destroyed the Akashi engine plant, leaving 275 Ki-61 fighters without any engines. With the B-29s ranging with near impunity over the home islands, the IJAAF headquarters, the Koko Hombu, suggested that the engineless Ki-61s be adapted to take the most readily available and reliable engine- IJAAF engineers suggested that Kawasaki find a way to fit the engineless fighters with the Mitsubishi Ha-112 radial engine, a 14-cylinder twin row radial engine comparable in power to the Pratt & Whitney R-1830 radial used on the Consolidated B-24 Liberator and the Douglas C-47 Skytrain/Dakota. 

Takeo Doi was initially not pleased with the Koku Hombu's directive to fit the Ha-112 to the Ki-61. The radial engine was 48 inches in diameter and the fuselage of the Ki-61 was only 36 inches in diameter. But seeing as to how there was little alternatives and the need for fighters great, Doi had his engineering staff work around the clock to make the Ha-112 work with the Ki-61 Hien. Fortunately Kawasaki was in possession of a Focke Wulf Fw 190 which had been delivered to the Japanese several years earlier for engineering study. Using the cowl and engine mount of the Fw 190 as a starting point, Doi and his team even replicated the horizontal alignment and collection of the exhaust pipes of the Fw 190 which in the Kawasaki design actually added between 6 to 9 mph of thrust augmentation to the aircraft's speed. Designated the Ki-100, the prototype aircraft made its first flight a mere three months after start of design work- a figure all the more incredible in light of the tremendous toll the B-29 attacks were taking on Japanese industry. By the time the third Ki-100 prototype took flight, the Koko Hombu was sufficiently impressed that all the engineless Ki-61s were ordered to be converted to Ki-100 standard. 

On many occasions, Ki-100s bested Hellcats and Corsairs.

"Sufficiently impressed" would be an understatement- the Ha-112 radial engine actually made the Ki-100 superior in every performance parameter to the Ki-61, much to the surprise of Takeo Doi. Although just slightly slower in cruise than the Hien, the Ki-100 was more maneuverable and had a faster climb rate. The IJAAF even took the Ki-100 prototypes into mock air combat against a captured P-51C Mustang. With the flight test program only lasting three weeks, the first Ki-100s went into combat with the 18th Sentai in Chiba on the same night in March that B-29s had laid waste to sixteen square miles of Tokyo in a firebombing attack. Less than six weeks elapsed since first flight to first combat! Production of the Ki-61 was terminated immediately and in less than three months all 275 engineless Ki-61s were rebuilt as Ki-100s AND the Kagamigahara factory also managed to build nearly 75 new-build Ki-100s that featured a cut back rear fuselage to improve aft vision for the pilot. As fast as Ki-100s could be built they were funneled straight to home defense units who found the Ki-100 a formidable fighter. Numerous large dogfights against Grumman F6F Hellcats and Vought F4U Corsairs found the Ki-100 on the winning side with more American fighters shot down than Ki-100s. By May 1945 the Ki-100 finally had met its match as long range P-51D Mustangs from Iwo Jima were now escorting the B-29s all the way to Japan and back. Dogfights with P-51Ds ended up swinging in favor of pilot skill and numerical advantage rather than any deficiency on the part of either aircraft. 

The one weakness of the Ki-100 was its high altitude performance as it lacked a turbocharger and as a result, few B-29s fell to the Ki-100. Work was underway for a supercharged high altitude Ki-100 when the war came to an abrupt end with the atomic bombing of Hiroshima and Nagasaki. Unfortunately for Japan, only about 500 Ki-100s were built before the war ended, but compared to other Japanese fighter designs, the Ki-100 proved to be Japan's finest fighter aircraft as a swansong for the once-feared IJAAF. From inception to the end of the war, the lifespan of the Ki-100 was barely ten months with an ad hoc marriage of engine and airframe out of necessity! The only surviving Ki-100 can be seen today at the RAF Museum. 

Source: Air International, October 1976, Volume 11, Number 4. "The Last Swallow of Summer: The Extraordinary Story of the Ki-100", p185-191.

The first pilots of the American Volunteer Group (AVG) arrived in the China-Burma-India combat theater in September of 1941, disembarking ships in Rangoon, Burma. Getting up to speed with General Claire Chennault's rigorous training program while battling supply problems sapped morale of the first Flying Tigers. While the main force of the AVG was based in Kumming, China, the Japanese occupation of French Indochina and subsequent arrival of Japanese forces in Thailand meant that the 750-mile Burma Road from Rangoon's port to Kumming was China's only real supply line to the outside world in their fight against the Japanese.

As a result, Chennault dispatched his 3rd Pursuit Squadron of the AVG back to Rangoon to support the small RAF Brewster Buffalo force of No. 67 Squadron already stationed there to defend the port city. On 23 December 1941 the Flying Tigers of the 3rd Pursuit Squadron went into action repelling a Japanese bombing raid on Rangoon- the AVG shot down 10 bombers and one fighter with a loss of four planes and two pilots. The Royal Air Force shot down three fighters but lost five Buffalos and their pilots.

Angered by their losses at what they thought were amateurs on the 23rd, a larger Japanese force of 60 bombers and 20 escorting fighters attacked on Christmas Day. The 3rd Pursuit Squadron mustered 13 Tomahawks (the most any AVG squadron had managed to do at once) and along with the RAF Buffalo fighters, their charged head-first into the large formation as it approached Rangoon.

The RAF shot down eight bombers but lost another five fighters and the rest of their Buffalo force was destroyed on the ground. The Flying Tigers, though, claimed 24 to 28 bombers (postwar research indicates that 10 were shot down, and another eight ditched in the sea off the coast of the city) with no losses to their own pilots. The 1941 Christmas Day air battle over Rangoon was the first time the Japanese faced serious aerial opposition and in post war interviews, the Japanese pilots reported being impressed with the aggressiveness and persistence of the Flying Tigers.

It marked a turn-around for the AVG and morale soared. Western newspapers reported on the success of the Flying Tigers at a time when the Allies were facing defeats on multiple fronts in Europe, the Mediterranean, and the Pacific. The Japanese Army Air Force had to adopt diversionary strikes which diluted the effectiveness of the main striking body. By the end of the month, the 3rd Pursuit Squadron was relieved by the AVG's 2nd Pursuit Squadron and they took an even more aggressive approach, raiding Japanese airfields in Thailand.

Source: Wings of Fame, Volume 9. Aerospace Publishing/AIRtime Publishing, 1997. "American Volunteer Group- The 'Flying Tigers'" by Robert F. Dorr, p6-13.