Yokosuka MXY7 Ohka Model 22 by BrenGun

Yokosuka MXY7 Ohka Model 22 by BrenGun
1/48 scale
Kit No. BRP48002
Cost: $19.99
Decals: One version – Imperial Japanese Navy
Comments: Engraved panel lines; photo-etched details and towing dolly included; one-piece canopy

History

In the Summer of 1944, a number of Japanese Naval officers of all ranks, increasingly concerned with the course of the war and the overwhelming material strength of the Allied forces advancing towards the Home Islands, began to advocate for the use of drastic new combat methods in light of the poor likelihood of staving off defeat by conventional means. One such officer was Ensign Mitsuo Ohta, a transport pilot serving with the 405th Kokutai, who conceived the idea of a rocket-propelled suicide aircraft that would be more or less invulnerable to interception.

With the help of personnel from the Aeronautical Research Institute of the University of Tokyo, Ensign Ohta proceeded to draft preliminary plans for his proposed aircraft, and in August 1944 submitted his drawings to the Dai-Ichi Kaigun Koku Gijitsusho at Yokosuka. Ensign Ohta’s proposal was favorably received by the Imperial Japanese Navy, which decided to proceed with the project and assigned the preparation of detailed drawings to a team of engineers led by Masao Yamana, Tadanao Mitsugi, and Rokuro Hattori.

Designated MXY7, the Ohka, or Cherry Blossom, was primarily designed as an anti-invasion or coastal defense weapon to be launched from a mother ship such as a twin-engined Mitsubishi G4M (Allied code name: Betty). Once released, after an initial glide, the Ohka was to accelerate towards its target with the help of three solid-propellant rockets mounted in the tail, fired individually or in unison. The tiny aircraft — it was just shy of 20 feet long, with a wingspan of slightly more than 16 feet, 9 inches — was built of wood and non-critical metal alloys. Great care was taken in its design to enable it to be mass-produced by unskilled labor.

Instrumentation in the cockpit was kept to a minimum, and good maneuverability was demanded to achieve reasonable accuracy in the attacks for which it was designed. By September 1944, ten MXY7’s had been built. Given the formal designation of Navy Suicide Attacker Ohka Model 11, the initial version carried a 1,200 kg (2,646 lb.) warhead in the nose, and was to be transported in the modified bomb bay of a G4M2e bomber (Navy Type 1 Attack Bomber Model l24J). The powerplant was three Type 4 Mark 1 Model 20 rockets, producing a combined thrust of 1,764 lbs. for 8-10 seconds. Unpowered and powered flight trials began respectively in October and November 1944. These were successful, demonstrating that the Ohka would achieve a top speed of 403 mph at full rocket thrust.

MXY7 K-1 Kai Two-seat trainers being inspected by U.S. Navy personnel. Powered by a single Type 4 Mk I Model 20 rocket motor, trainers were fitted with flaps and landing skis. Two were built at Yokosuka. Source: U.S. Navy via Smithsonian Institution

Meanwhile, the Imperial Japanese Navy had put the Ohka into full production without waiting for the conclusion of the trials, and a total of 755 machines were completed by March 1945. On March 21, 1945, the Ohka had its combat debut with the 721st Kokutai, but the sixteen G4M2e mother ships were intercepted and forced to release their Ohkas short of the target. This highlighted the critical weakness preventing the Ohka from being a more effective weapon: Because of its short range, it was dependent on other, slower aircraft to get into the target area — and those aircraft were often vulnerable to enemy fighters. By this stage of the war, Japan’s fighter force had been bled white, and was unable to provide systematic, effective escort for Ohka missions. On April 1, 1945, the United States invaded Okinawa, the southernmost of the Japanese Home Islands, just over 400 miles from the nearest land mass in the chain. This day marked the Ohka’s first success, when they damaged the battleship West Virginia and three transport vessels. An Ohka also sank the destroyer Manner L. Abele off Okinawa on April 12th.

A detailed schematic of the Ohka drawn up by the Navy’s Technical Air Intelligence Center in 1945. While frequently unsuccessful, the appearance of the Ohka during the invasion of Okinawa caused such concern that the Office of Naval Intelligence was charged with learning as much about it as soon as possible. The name “Baka,” Japanese for “Fool,” was assigned by the Americans in an attempt to minimize the Ohka’s significance, but it was a factor in the concerns about high American casualties had an invasion of the Japanese Home Islands been necessary to force a surrender.

Due to the MXY7 Model 11’s critical flaw – short range, production of the type ceased in March 1945, even before its first use in combat. Forty-five examples of an unpowered glider version, dubbed the Ohka K-1 (see photo above), were produced for training purposes. These replaced the warhead in the nose with water ballast to duplicate the handling characteristics of the armed versions, with the pilots being able to release the water ballast in the last stages of flight to reduce the landing speed as the trainer came in on specially mounted skids.

The Ohka Model 22 was planned as an improved version of the Model 11. The Model 22 was longer than the Model 11, but with a shorter wingspan [Edtor’s Note: While R.J. Francillon in his important work, Japanese Aircraft of the Pacific War, reports that the Model 22 was a smaller aircraft than the Model 11 with a smaller warhead of 1, 323 llbs., comparing the Brengun Model 22 kit to the Fine Molds Model 11 in the same scale, the Model 22 does in fact have a shorter wingspan but is clearly longer, with a good portion of the additional length apparently in the nose forward of the leading edge of the wings — implying the presence of a potentially larger warhead].

The Model 22 addressed the key deficiency of the Model 11, featuring increased range due to the installation of a Campini-type jet engine with a 100 hp Hitachi four-cylinder in-line engine as a gas generator. The intakes for the jet engine are clearly visible on the sides of the Model 22’s fuselage aft of the cockpit. Fifty of these new aircraft were delivered by the Dai-Ichi Kaigun Koku Gijitsusho, and a test flight was completed in July 1945 which proved fatal for the pilot when auxiliary rockets installed under the wings went off accidentally, causing a stall from which he could not recover. Plans were also developed for a larger version, dubbed Model 33, powered by an Ne-20 turbojet and carrying a 1,720 llb. warhead. The Model 33 was to be carried into battle by the Navy Attack Bomber Renzan (G8N1), which was faster than Mitsubishi’s G4M, but the low priority accorded G8N1 production doomed the Model 33. Yet another version, the Model 43A, was to be still larger and catapulted from the decks of surfaced submarines, and the Model 43B was similar to the 43A and would have been catapulted from caves in an invasion of the main Home Islands.

While an impressive technological achievement, the Ohka proved to be of little strategic value due to the critical deficiency of the Model 11’s poor range, and the ending of the war before the improved Model 22 could be perfected.  The yet more advanced versions never left the drafting boards. While the Japanese worked hard to develop the Ohka into an efficient weapon, the atomic bombings of Hiroshima and Nagasaki ended the need to overcome the rocket plane’s engineering challenges. Highly recommended for those who appreciate detailed late war Kamikaze weapons.

The Kit

Brengun’s Ohka comes in a resealable plastic bag on a single sprue. It is injection molded in tan and consists of just 43 plastic parts, including parts for the dolly and the clear plastic one-piece canopy. The simplicity of the aircraft itself is underscored by the fact that the towing dolly accounts for 19 of the parts. There is also a small photo-etch fret with five additional brass parts for a front sight assembly and rear antenna. Of special note is the fact that a 10-gram nose weight is recommended and clearly illustrated in the instructions, despite the Ohka’s lack of landing gear, as it may be a bit tail-heavy once situated on the dolly.

The moment of attack: Few Ohkas reached this point, as most were still attached to their mother ship Mitsubishi G4M “Betty” bombers when the latter were shot down by American fighters outside the Ohka’s effective range.

There are delicate engraved panel lines on the fuselage, and rather heavier ones for the control surfaces on the wings and tail. The cockpit is relatively spare, with a bare seat, floorboard with minor raised detail, control yoke, and instrument panel, which with its raised relief for the dials is the most detailed component by far. Internal sidewall framing is also molded into the fuselage interior. Directly behind the seat is the rear bulkhead, and there is a single circular part aft of that, depicting the exhaust fan blades and cone.  The stubby wings consist of two parts each, and the three piece tail assembly looks utterly trouble-free, even with two antennae that will have to be attached, one of which is a photo-etch part. There is no special detail for the intakes at the rear of the fuselage, and on the actual Model 22 there may not have been much to see in terms of any inner workings.

Although there is a rudimentary paint guide consisting of seven colors, it is not coded to any particular manufacturer, and calls out colors in the clear: Wood, Black, Gunmetal, Dark Grey, etc. The instructions include no paint guide whatsoever for the aircraft itself, but the rear of the box does provide a three-view color schematic revealing that the Ohka was painted in IJN Grey overall with a Burnt Iron jet exhaust.

Markings

The kit decals are quite glossy and very crisply registered. They are relatively few and consist of cherry blossom markings, together with a series of stencils in Japanese and red stripes. Interestingly, the Japanese did not bother with national markings on this particular Kamikaze weapon, perhaps because it was purpose-built for the task.

Conclusion

Overall, Brengun’s no-nonsense approach to this kit would seem to make it an excellent prospect for a weekend build. It is crisply molded with a modicum of detail, and nothing about it threatens to bog the modeler down or delay completion. Highly recommended.

An Ohka with the fuselage stripped down to reveal the rocket motor and the large naval artillery shell that served as its warhead. Source: U.S. Navy; Public Domain.

Reference

Japanese Aircraft of the Pacific War by R.J. Francillon; Copyright 1970, Putnam & Company; London