In the summer of 1941, by order of Koku Hombu at the Rikugun Kokugijutsu Kenkyujo Army Aviation Research Institute, research began on the creation of a heavy twin-engine fighter. A team of specialists from several Japanese aircraft manufacturing companies was created at the institute. It was initially assumed that the new aircraft would be a single-seat long-range escort fighter. However, in July 1942, the design team was disbanded, and the engineers from its various companies were recalled to solve more urgent tasks.

It was decided to retask the machine as a heavy multi-purpose attack fighter designed for operations at low and medium altitudes and at the same time capable of hitting heavily armored ground and surface targets. To speed up work, several engineers from the 1st Army Aviation Arsenal located in Tachikawa were sent to the institute. Based on new tasks, it was decided to equip the aircraft with a cannon, large for aviation, 57-mm Ho-402 caliber, specially developed for this aircraft by Nippon Special Steel Dr. Masaya Kawamura.

The development of a new automatic gun, which received the designation No-402, went in parallel with the Ki-93 project. At the same time, Nippon Special Steel worked closely with Rikugun. The entire project of the attack aircraft was built around this gun, and the gun was created for the aircraft project. The No-402 cannon was located in a ventral gondola.

The Ki-93 was a low-winged monoplane of all metal construction, with the crew of two sitting in tandem under a canopy at the front of the fuselage, and a ventral gondola slung under the fuselage to accommodate large cannons. The wing was of laminar flow section.

On February 22, 1943, the new aircraft project was approved by Koku Hombu and received the designation Ki-93.

By the time the Ki-93 had already begun to take shape, the military situation in Japan was already very difficult. Japan suffered from the almost daily B-29 raids, and the US invasion of Japan loomed ever more clearly on the horizon. It was urgently necessary to seek means of fighting both the almost invulnerable B-29s and the anticipated Allied invasion fleet. As a result, the Ki-93 could become one and the other. When Rikugun Kokugijutsu Kenkyujo set about shaping the final look for the future Ki-93, the idea came up that the aircraft being designed could solve both anti-bombing and anti-ship missions equally well. In both cases, the aircraft had to be well protected in order to keep inevitable damage from both defensive fire of bomber machine guns and anti-aircraft artillery of ships. Therefore, it was supposed to build two versions of the Ki-93 in parallel. First, the Ki-93-I Co. is a heavy interceptor fighter. The second Ki-93-I Otsu is an anti-ship attack aircraft. Initially, it was planned to install Mitsubishi Ha-211 engines on the aircraft, but subsequently both models were equipped with two 18-cylinder air-cooled Mitsubishi Ha-214 engines, each of which developed 2,400 horsepower, for the most efficient removal of tremendous moment from engines equipped with six-bladed propellers 3.8 m in diameter

To ensure maximum survivability, the pilot was protected by five 12 mm armor plates. Two armor plates protected the cockpit in front, two on the sides and one on the back. Glazing of the cockpit was made of 70 mm bulletproof glass. The rear gunner was also protected by 12 mm of armor from the tail side of the aircraft. In addition, the fuselage fuel tanks were designed, had automatic fire extinguishing means, and were also protected by 8 mm armor. Each engine also had local armor protection. Defensive armament consisted of one 12.7-mm machine gun Ho-103, located in the rear of the cabin under the movable section of the flashlight. The difference in the two versions of the Ki-93 was the type of gun mounted in the lower gondola.

The Ki-93-I Co. was equipped with a 57-mm Ho-402 cannon with 30 rounds, reinforced with two 20-mm No-5 guns. It was expected that the 57-mm gun No-402 is capable of inflicting enough damage in one shot, guaranteed to destroy the B-29. But-402 had a rate of 80 rounds per minute, firing 2.7-kg shells with an initial speed of 700 m / s. For Ki-93-I Otsu, they provided weapons from the latest automatic 75-mm gun No-501, the total mass of which was 450 kg, the rate of fire reached 80 rounds / min, the initial projectile speed 500-550 m/s.

In addition to the Ki-93-I gun, the Otsu had to carry two 250 kg bombs. In the manufacture of prototypes, it turned out that it was not possible. This was due to a greater than expected weight of equipment. In order to somehow rectify the situation, the ammunition load of the No-402 gun had to be reduced from 30 to 20 rounds. Additional difficulties were brought by the undeveloped Na-214 engines, which lacked the declared power. As a result, the first prototype in the Ki-93-I Co. configuration was completed only in March 1945. On 8 April 1945 pilot Lt. Moriya of the Koku Shinsa-bu (Air Examination Department) with 2nd Lt. Ikebayashi in the second seat, first flew, from Tachikawa airport. During the tests, the armament was absent.

The first 20-minute flight turned out to be the last. When landing with too high landing speed, undershot the runway,and the left landing gear broke, resulting in severe damage to the left wing, prop, engine and landing gear. The only flight noted good controllability, good flight characteristics, and all on-board equipment worked flawlessly.

The prototype was returned to the factory for repair, which took four weeks. When the aircraft was ready for re-testing, an American bombing raid on the city of Tachikawa, completely destroyed the aircraft.

The second prototype Ki-93-I Otsu on the eve of the surrender of Japan was in the final stages of assembly.

After the raid on Tachikawa, it was evacuated to the Takahagi airfield in Saitama Prefecture, complete the assembly and make a test flight. Here, the incomplete prototype was captured by the Americans. After the war, he was taken to the United States as FE-152 at Middleton Air Material, where it was studied in September 1946. On 18 September 1946 was it was transported to Park Ridge, where all trace was lost after 1949.

Ki-93-Ia
Engines: 2 × Mitsubishi Ha-214 1, 1,470 kW (1,970 hp)
Propellers: 6-bladed VDM, 3.80 m (12 ft 6 in) diameter
Wingspan: 19.00 m (62 ft 4 in)
Wing area: 54.75 m2 (589.3 sq ft)
Length: 14.215 m (46 ft 8 in)
Height: 4.85 m (15 ft 11 in)
Empty weight: 7,686 kg (16,945 lb)
Gross weight: 11,440 kg (25,221 lb)
Crew: 2
Guns:
1× 57 mm Ho-401 cannon in ventral gondola
2× 20 mm Ho-5 cannon in wing roots
1× 12.7 mm Ho-103 machine gun on flexible mounting in rear cockpit
Estimated performance
Maximum speed: 624 km/h (388 mph, 337 kn) at 8,300 m (27,200 ft)
Cruise speed: 350 km/h (220 mph, 190 kn) at sea level
Range: 3,000 km (1,900 mi, 1,600 nmi)
Service ceiling: 12,050 m (39,530 ft)
Time to altitude: 9 min 3 sec to 6,000 m (19,700 ft)