CHECK SIX: Ships Sunk or Damaged by the Yokosuka MXY7 Ohka

Hasegawa model kit box art showing a G4M releasing an Ohka
(Hasegawa Models)

The Yokosuka MXY7 Ohka ("Cherry Blossom") kamikaze flying bomb was conceived by Ensign Mitsuo Ohta of the 405th Kokutai of the Imperial Japanese Navy. He was considering how to overcome the dense anti-aircraft defenses of Allied warships. His design solution, aided by students from the University of Tokyo, was for a rocket propelled kamikaze aircraft that would be flying too fast in its terminal approach to the target to be shot down. He submitted his ideas to the IJN for consideration and his proposals were refined further by engineers at the IJN's Yokosuka Naval Air Technical Arsenal which resulted in the MXY7 design which was essentially an anti shipping missile with a 2600 lb warhead with a kamikaze pilot as its guidance system. 

The Ohka had three rocket engines which could be ignited at once or in sequence. Dropped by the Mitsubishi G4M "Betty", the Ohka had a range of approximately 23 miles and had a terminal approach speed between 580-620 mph, significantly faster than piston engined kamikazes. 

The Yokosuka arsenal would build 155 Ohkas while the Kamisagura Air Arsenal would built over 600 Ohkas. It was planned to debut the Ohkas at the Battle of Leyte Gulf, but the ships transporting the Ohkas to the Philippines were sunk enroute. The Ohka's operational debut would be in the Battle of Okinawa with mixed results:

12 April 1945: USS Mannert L. Abele, destroyer, sunk by one, possibly two Ohkas.

12 April 1945: USS Jeffers, a destroyer converted to a minesweeper, damaged.

12 April 1945: USS Stanly, a destroyer, damaged.

4 May 1945: USS Gayety, a minesweeper, damaged.

4 May 1945: USS Shea, a light destroyer coverted to a minelayer, damaged.

11 May 1945: USS Hugh W. Hadley, a destroyer, damaged.

Interestingly, the captain of a support vessel who witnessed the sinking of the USS Mannert L. Abele had this to say: "It is difficult to say what it was that hit the DD 733. This officer personally saw what appeared to be two (2) planes orbiting in a northerly direction from the DD 733, and then suddenly, what appeared to be, one plane, accelerated at a terrific rate, too fast for us to fire at. This plane dove at an angle of approximately 30 degrees, starting at about four miles [7.5 km] away. Since we had no air search radar, the above statements are merely my own conclusions."

That captain's report was the first to indicate that the Ohka was operational. 

Further reading:

The Coming Kamikaze Threat We Never Faced

The 1937 Kamikaze Flight That Didn't End in a Fiery Crash

Task Force 38's Unheralded Contribution to the Fall of Japan

CHECK SIX: The 1937 Kamikaze Flight That Didn't End with a Fiery Crash

"CHECK SIX" is new little feature I'm going to be introducing here and there here at Tails Through Time as a little filler in-between my primary articles. The name for this feature is because they're going to be quick looks back in aviation history that don't necessarily warrant my more in-depth articles. The titles for these short tidbits will always start off with "CHECK SIX". 

This particular Mitsubishi Ki-15 with the registration J-BAAI was the first Japanese aircraft to fly to Europe when it left Tokyo on this day (April 6) in 1937 for a oodwill flight to London Croydon Airport. Sponsored by the Asahi Shimbun newspaper as part of the celebrations for the coronation of King George VI, the plane was named "Kamikaze-go" and flew Tokyo-Taipei-Hanoi-Vientiane-Calcutta-Karachi-Basra-Baghdad-Athens-Rome-Paris-London. The pilot, Masaaki Iinuma, was only 26 at the time and both he and his navigator, Kenji Tsukagoshi, were awarded the Legion of Honor by the French. 

Total elapsed time from departure in Tokyo was 94 hours, of which 51 hours were actual flying time. Iinuma later served as a test pilot in Japan and was killed in action in December 1941 in Cambodia. The navigator, Tsukagoshi, was on the Tachikawa Ki-77 prototype when it set of for a flight to Germany from Singapore in 1943, but the Ki-77 disappeared over the Indian Ocean. 

The Japanese classical music composer Hisato Ohzawa wrote the Piano Concerto No.3 "Kamikaze" in honor of this record breaking flight. If you're a fan of the composer Sergei Prokofiev, Ohzawa's work is in that Impressionistic style. 

(Photo: Wikipedia)

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

In the fall of 1943, the Japanese military liaisons in Germany were given a demonstration of the Messerschmitt Me 163 Komet rocket fighter. They sent back enthusiastic reports on the potential of the Me 163 in defending against the predicted USAAF strategic bombing offensive that would start the following year. Despite their reports and the enthusiasm of some in the Japanese military of what the Komet might offer in the defense of the Home Islands, most of the Japanese military command had reservations about putting the Komet into service as the Japanese industry would have to master the production of large quantities of hydrogen peroxide and hydrazine. Synthesizing the two rocket fuels used by the Komet would require a significant amount of electrical power. Others in the military command questioned whether the Komet's short endurance was a liability, particularly as a point-defense fighter it would have reach up to higher altitudes to attack the B-29 Superfortress than the altitudes over Europe where the Komet's main prey were unpressurized B-17 Flying Fortresses and B-24 Liberators. Despite legitimate questions about the practicality of the Komet, negotiations for license production in Japan of the Me 163 proceeded which included not just the Komet airframe but also the Walter HWK 509A bi-fuel rocket motor. By 1 March 1944, the approval was reached and the Germans would supply Japan with complete blueprints and manufacturing data for the Me 163B variant as well as one complete airframe, two sets of sub-assemblies, and three complete rocket motors. A Japanese joint-service mission with Army and Navy representatives would also be sent to Germany to observe not just the manufacture of the Komet but also learn the procedures for operational use. As it was, events in Europe would keep the joint-service mission from arriving, but two Imperial Japanese Navy submarines were used to bring the cargo back home to Japan as a measure of redundancy in case one submarine was lost on the return voyage. The first submarine to depart was the former U-1224 which was handed over to the Japanese in February 1944 and named "Satsuki". The second submarine was I-29 "Matsu". 

The Mitsubishi J8M1 Shusui. This one was brought to the US after the war.

The Satsuki was sunk in the Atlantic by the destroyer escort USS Francis Robinson which was operating as part of the escort carrier USS Bogue's hunter-killer group. The Matsu, however, was able to reach Singapore on 14 July 1944 and its cargo was quickly flown to Tokyo for analysis. The staff of the 1st Naval Air Technical Arsenal met regularly at the naval base of Yokosuka to discuss whether to launch production of a Japanese Komet. The Battle of the Philippine Sea (the "Great Marianas Turkey Shoot") had just taken place which had all but eliminated Japan's carrier fleet. With the imminent capture of the Marianas, it was only a matter of time before B-29 bases within easy reach of the Home Islands became operational. Despite the decline in Japan's war fortunes that summer, many in the daily discussions were wary of committing Japan's industrial resources to so radical a weapon. The balance was tipped in favor of production when the commander of the Yokosuka arsenal decided in favor of the aircraft, stating something to the effect that desperate times would call for desperate measures. 

Mitsubishi had been assigned the task of building the Komet as the J8M, but they refused to proceed with so much discord within the Japanese military command on the practicality of the aircraft. On 27 July 1944, a joint Army-Navy commission formally ordered the aircraft from Mitsubishi as the J8M Shusui ("Sword Stroke"). This is significant for Mitsubishi as the Imperial Japanese Navy and the Imperial Japanese Army took inter-service rivalry to new degrees that made the US armed services rivalry look like a minor disagreement. For both the IJN and IJA to jointly pursue a single design was nearly unprecedented and sent a message to Mitsubishi that they were serious about wanting a Japanese Komet. The Navy designation was J8M and the Army designation would be Ki-200 (though J8M is the more commonly referred to designation for the Shusui). From that point, the program took on a more serious effort and urgency. The cockpit mockup was reviewed on 8 September 1944 and the full scale mockup of the Shusui was reviewed 18 days later. A joint Army-Navy production schedule was drawn up with 155 aircraft to be delivered by March 1945, 1,300 by the following September and no fewer than 3,600 delivered by March 1946. Because of the loss of one of the submarine and the fact that joint-service commission never made it Germany to observe production, the Mitsubishi team had to make some educated guesses during the design process in preparing the Shusui for production. In addition, some of the basic equipment like batteries and radios were sized and weighed differently in Japan compared to German equipment, and this in turn affected not just airframe structure but also weight and balance of the aircraft. 

Pilot (possibly Cdr Inuzuka) in front of the Akikusa trainer.

In addition, the Shusui would have been the first tailless aircraft to be flown in Japan, so it was decided that the Yokosuka arsenal would build training gliders that were essentially unpowered Shusui aircraft. These gliders were designated MXY8 Akikusa ("Autumn Grass") and the first Akikusa glider was flown on 8 December 1944. The second Akikusa glider built was delivered to the Army for their own flight testing. On 1 December, the first structurally complete Shusui was reviewed and approved by both the Army and Navy. However, misfortune struck the program when an earthquake damaged Mitsubishi's plant in Nagoya and then a few days later the area was struck by B-29 Superfortresses. Despite the setbacks, Commander Toyohiko Inuzuka, who flew the first Akikusa gliders, made the first unpowered flight of the J8M Shusui on 8 January 1945. Other pre-production aircraft were test fitted with rocket motors while the unpowered Shusui flight test program continued. 

Mitsubishi was also responsible for getting the rocket motor which was designated Toku Ro.2 into production, but on the day of the first bench test of the motor, B-29s attacked the plant. Numerous technical problems mounted in the motor development as the Japanese had to substitute some materials for others in the design which would later turn out to be unsuitable for a production motor. By April 1945, the Shusui aircraft were ready but the rocket motor program was already 3 months behind schedule. It was decided if the Toku Ro.2 could run for just two minutes, they'd attempt the Shusui's first powered flight on 22 April, but the engine exploded during a ground test. B-29 attacks exerted their toll on the program with the engineering groups having to move to new facilities periodically. Eventually two groups were set up, each tasked with getting the Toko Ro.2 running. By June, one group had their motor on the bench running four minutes and the other group had their motor bench tested to three minutes. It was decided that these bench tested motors would be used for the Shusui's first flight. Ground runs continued to reveal problems with the motor and it wasn't until 5 July 1945 that they were ready for the first powered flight. 

Preparing for the J8M1's maiden flight or a ground test run.

On 7 July 1945, Toyohiko Inuzuka started up the motor for the first Shusui powered flight. After an 11-second takeoff run, the Shusui became airborne and jettisoned its takeoff dolly as planned. At 1,150 feet, Inuzuka began to have engine problems as the motor began to sputter and then quit. He was able to reach 1,640 feet, where he leveled off and turned for the glide back to Yokuku Airfield. Releasing his remaining fuel via emergency release valves, he realized he had made too many S-turns and was going to come short of the airfield. Aware he was about to hit a house on the airfield perimeter, Inuzuka deliberately stalled the Shusui by abruptly pulling the nose up. The aircraft cartwheeled and missed the house, but it was destroyed and Inuzuka would die a few days later from his injuries. Analysis showed that he suffered fuel starvation during his climb- the acceleration and his angle of climb caused the fuel to slosh back and recede from the tank outlet. A few days later, two other motors that were being bench tested for the flight test program exploded. This left only one complete rocket motor that had been tested and this one was in the possession of the Army for the installation in their Shusui prototype. As the Army and Navy struggled to get the program back on track, Hiroshima was bombed on 6 August and three days later on 9 August Nagasaki was bombed. Six days later, Japan unconditionally surrendered. 

The IJAAF's Ki-202 Shusui-Kai

On the day of surrender, there were four finished J8M Shusui airframes and six more nearing completion on the assembly line. Four production Toku Ro.2 motors had been finished and were ready for testing with two nearing completion with components for another 20 motors ready. On the day of the surrender, the Navy was looking at a powered version of the MXY8 Akikusa training glider to allow longer sorties as well as to incorporate water ballast to better simulate a fully fueled Shusui. While both services were committed to producing a common aircraft, the Navy was already working on the J8M2 Shusui-Kai which deleted one wing cannon for an extra fuel tank to give it more endurance. Even more ambitious, the Army was working on their own Shusui-Kai variant designated Ki-202 which was a substantial redesign of the Me 163B that was longer with more endurance. The Army had planned to use the Ki-200 (J8M) as an interim type until they could put the Ki-202 in service starting in 1946. 

From a model kit- the ones one the right are "what if" in service schemes

Three J8M Shusui aircraft survived the war. Two of them were captured by US occupation forces and shipped to the United States. One was on display at NAS Glenview in Illinois but was scrapped on site in 1946. The other one is on display today at the Planes of Fame Museum in Chino, California. The third airframe was discovered in a cave in the 1960s in poor shape. It was on display for a while at Gifu AB where the JASDF's Air Development and Test Command is based. In 1999, Mitsubishi restored it and has it on display at their museum at their Komaki plant. While the story of the J8M is short and full of tragedy, when you consider that between the time the I-29 "Matsu" docked in Singapore with its precious cargo and the Japanese surrender, one year, one month, and one day elapsed. In that time despite the strain on Japanese industry by the B-29 attacks, they were able to get one aircraft to fly once, even though it did end badly. In his 1976 Air International article on the Shusui, author Yoshio Imagawa observed that "of Japanese national character that fanaticism and fatalism are innate ingredients." Given the growing desperation of the Japanese military in 1945, having their own version of the Messerschmitt Me 163 Komet seems almost pre-ordained. 

Source: "Japan's Final Sword Stroke...The Story of Shusui" by Yoshio Imagawa. Air International, Volume 10, Number 6. June 1976, pp 283-288. Images: Wikipedia, Koku-Fan, Japanese aviation forums. 

Tactics Over Technology: The Thach Weave

One little known aspect of the June 1942 Battle of Midway was that it wasn't just the turning point in the Pacific War that started to roll back the Japanese Empire, but it also was a turning point in fighter tactics that changed the way air combat was conducted. At the start of the Second World War, US Navy fighter squadrons had eighteen aircraft that were divided into six sections of three planes each- each section was composed of a flight leader and two wingmen. However, well before the attack on Pearl Harbor, the Navy fighter squadrons VF-2 and VF-5 experimented with two-plane sections with a flight leader and a single wingman. In a three-plane section it was found that the wingmen tended to focus too much on formation keeping instead of being on watch for enemy aircraft. The shift to a two-plane section with the wingman staggered and below the lead's altitude lessened the need for strict formation keeping. As a result, the two-plane section became the basic unit of the Navy's fighter squadrons beginning in July 1941. Three sections then made up a division in the squadron for a total of six planes- in cruising, each of the three sections flew in trail, but nearing combat they assumed an echelon formation. Having the support of a single, more vigilant wingman improved the odds of survival particularly against the superior Mitsubishi A6M Zero fighter.

That summer, Lt. Commander John "Jimmy" Thach, commander of VF-3, was still stateside and undergoing conversion with the rest of his squadron in California from the troublesome Brewster F2A Buffalo to the more robust Grumman F4F Wildcat. While there, Thach had access to preliminary reports from the American Volunteer Group "Flying Tigers" in China on the phenomenal performance of the Japanese Zero, possesing maneuverability and a rate of climb well in excess of their new F4F Wildcat mounts. At the time Thach was already well-known to his men for using matchsticks on a table to come up with new tactical ideas for his aircraft. Now he was back to his kitchen table each night, playing with matchsticks trying to come up with a tactic to counter the exceptional maneuverability of the Zero. Thach's first conclusion was the standard three-section division was unsuitable. It was better to use just two sections with a total of four planes. But how to use them? Thach would deploy two sections of Wildcats flying abreast of each other at a distance that approximated the turning radius of the Wildcat. Because of their positioning abreast and at a distance, each section had a good view of the other section's six-o'clock position. When Zeroes engaged, they'd be forced to choose one section to attack and could be spotting by the other section. This is one key characteristic that set apart what Thach called his "beam defense position" from other similar weaving tactics- a commitment to be on lookout for the other section. 

Once a section was attacked, the other section either signaled the other one or just turned in towards that section under attack. Once alerted, the section under attack turned towards the incoming section. If the Zero pressed its attack, it faced a head on attack from the incoming section and if it withstood that, it would find itself in a position with the incoming section having another firing pass as each section weaved in and out from each other. If the Zero broke off the attack, then it faced having the incoming section getting on its tail. Thach also considered that the weave could also work on with just a single section if one fighter was engaged, the other fighter in the section could set up the weave. Wanting to prove it worked, Thach decided to test his ideas with the pilots of VF-3. Four planes were to play the part of the defenders flying in two sections. Thach was one of them. Another group of squadron pilots would play the part of the attackers- in his tests, Thach selected his best pilot, future Medal of Honor winner Edward "Butch" O'Hare, to lead the attacking group. To simulate the performance advantage of the Zero, Thach and the "defending pilots" would limit their Wildcats to just 1/2 power while O'Hare and the attacking pilots would get to use the full power of their Wildcats. Instructed to attack from different angles and altitudes, O'Hare found that once the "defenders" set up the weave from their beam defense position, they always found themselves facing the guns of one section or the other irrespective of their performance advantage. 

At the Battle of Midway, VF-3, led by Thach, were embarked on the USS Yorktown. Tasked with covering a group of plodding Douglas TBD Devastators, Thach was leading two sections at higher altitude. When the Devastators were jumped by Zeroes, Thach was unable to fly to their aid as his group had also been attacked by a group of Zeroes. In their initial firing pass, one of the four Wildcats was downed, but Thach had the remaining Wildcat set up a weave with his section. In short order, three Zeroes were shot down as the Zero pilots tried to aim on the weaving Wildcats and found themselves exposed to Thach and his men on repeated firing passes. Although Thach wasn't able to save the Devastators, the "Thach Weave" proved its worth in battle and word spread amongst Wildcat pilots that they now had a tool with which to fight the much-vaunted Zero. 

Thach's tactical genius was recognized after Midway and later in the war developed what was called the "Big Blue Blanket" defense against kamikaze attacks which was a layered defense using round-the-clock combat air patrols of Grumman F6F Hellcats and Vought F4U Corsairs as far away as possible from the carrier to catch the kamikazes early. Fighter sweeps were conducted over Japanese airfields to prevent kamikazes from getting airborne, and destroyer radar pickets were stationed as far as 50 miles from the main carrier force. During the Korean War Thach commanded the carrier USS Sicily and then after the war, captained the USS Franklin D. Roosevelt. In 1959 he was assigned to the Navy's antisubmarine warfare development unit with the ASW carrier USS Valley Forge as his flagship. His contributions to ASW tactics were so significant he was featured on the cover of Time Magazine and the Thach Award was later established for the best ASW squadron in the Navy. The Perry-class frigate USS Thach (FFG-43) is named in his honor. 

But he is best known for the Thach Weave and basic principles of the weave are still in use to this day in modern fighter combat. The Thach Weave was also used by Doulgas SBD Dauntless dive bombers in the Pacific- being much slower, the Dauntless were vulnerable to the Zero as well, but by employing the Thach Weave, the rear gunner of the Dauntless, having twin machine guns at his disposal, would have a much clearer shot at the attacking Zero during a weave. 

Source: United States Naval Fighters of World War II in Action by Michael O'Leary. Blandford Press, 1980, p62-63.

The Northrop Gamma started out in 1933 as a private venture involving the latest advances in structural techniques that influenced later generations of aircraft. Later to be designated the A-17, the last military version to bear the name Gamma was the Gamma 5. Only three were built before Northrop switched over production the A-17.

The first Gamma 5 was sold with US government approval to Japan in October 1935. Shipped to Japan the following month, it was evaluated by both Mitsubishi and Nakajima on behalf of the Imperial Japanese Navy and designated the BXN1.

The third Gamma 5 was shipped (again with US government approval) to the Imperial Japanese Navy and designated by the IJN as the BXN2. It was then turned over to Nakajima for further evaluation and is believe to have influenced the design of the Nakajima B5N "Kate" torpedo bomber.

Source: Aerospace Modeler Magazine, No. 7/Summer 2007. "The Northrop Military Gamma Family: Part 1" by Geoff Hays, p36.