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Mitsubishi Ki-51 (Sonia)

Imperial Japan (1940)
Picture of Mitsubishi Ki-51 (Sonia) Ground Attack / Reconnaissance Aircraft

While proving serviceable in the ground attack role, the Mitsubishi Ki-51 Sonia was relegated to kamikaze attacks by the end of World War 2.

Detailing the development and operational history of the Mitsubishi Ki-51 (Sonia) Ground Attack / Reconnaissance Aircraft.

 Entry last updated on 5/10/2016. Authored by Staff Writer. Content ©

Mitsubishi lent its considerable development and production talents to more than just "Zeroes" during World War 2. The Mitsubishi Ki-51 was an early-war low-wing monoplane intended for the light bomber/dive bomber role and was deployed by the Imperial Japanese Army (IJA) for a time in the conflict - particularly during actions over China and Burma. Total production eventually netted 2,385 examples and the type served into the final weeks of the Pacific War in August of 1945. The Ki-51 was codenamed "Sonia" by the Allies. Its formal IJA designation was "Type 99 Assault Plane".

The series began as two prototypes with a first flight recorded during 1939. From this came eleven pre-production aircraft for evaluation. Its design incorporated a crew of two seated in tandem under a long greenhouse-style canopy with the pilot in front and a gunner in back. The cockpit sat ahead of midships and over the monoplane wing assemblies which themselves were straight projections with rounded tips. The large radial piston engine was mounted in a forward compartment as usual and the fuselage tapering elegantly to a point under the tail. A single rounded vertical tail fin was used along with low-set horizontal tailplanes. The undercarriage was of the tail-dragger arrangement and fixed in place with aerodynamic fairings set over the main legs - typical of early-war mounts such as the Ki-51. Dimensions included a length of 9.2 meters with a wingspan of 12 meters and a height of 2.7 meters. Empty weight was 4,130lbs with a Maximum Take-Off Weight (MTOW) of 6,415lbs.

Power came from a single Mitsubishi Ha-26-II series 14-cylinder, air-cooled radial piston engine developing 950 horsepower. The engine drove a three-bladed propeller unit at the front of the aircraft and featured a large spinner for airflow. Maximum speed reached 265 miles per hour with a range out to 660 miles and a service ceiling up to 27,130 feet.

Standard armament included 2 x fixed, forward-firing 7.7mm Type 89 machine guns. The rear operator managed a single 7.7mm Te-4 series machine gun installation on a trainable mount. As a light bomber-dive bomber airframe, the Ki-51 was cleared to carry up to 440lbs of bombs.

Both Mitsubishi and the Tachikawa Army Air Arsenal contributed the impressive numbers of Ki-51 produced. Mitsubishi eventually delivered 1,462 of the stated total with Tachikawa adding a further 913 examples. The Imperial Japanese Army Air Force (IJAAF) became its primary user. All production models fell under the simple designation of "Ki-51".

In the early-going, such aircraft were crucial to the Japanese expansion in the Pacific, particularly against lesser foes where the Ki-51 could act with impunity. The Ki-51 served in the general light bombing role by delivering conventional drop ordnance where needed and doubled as a dive-bombing platform for more accurate strikes on enemy targets and positions. The machine guns could be used as a defensive measure or during strafing runs as needed. The structure of the aircraft proved robust enough that Ki-51s were operated from rough fields which broadened the tactical flexibility of this Mitsubishi design for Japanese warplanners. Later versions were up-gunned by having their 7.7mm machine guns replaced by 2 x 12.7mm Ho-103 series heavy machine guns for a better frontal "punch".

The success of the Ki-51 began to bring about another form, this of a tactical reconnaissance platform constructed by the Mansyu Airplane Manufacturing Company of Manchukuo (a subsidiary of Nakajima). The aircraft incorporated such modern qualities as a retractable undercarriage and three prototypes served as the start of the product. However, the design - designated as Mansyu Ki-71 - was not adopted for serial production.

Fortunes for the Japanese Empire changed after successes found the Allied advance in their drive towards Tokyo. Desperate to turn the tide of the war - or at least engage the allies in favorable surrender terms - stocks of Ki-51 aircraft were reconstituted later in the war for the kamikaze suicide role against Allied warships. For these suicidal endeavors, the aircraft carried an ordnance load of 550lbs to maximize damage and carnage against the enemy. Such ended the wartime career of the Ki-51 as the Japanese surrendered in September of 1945.

The Ki-51 existed in the post-war years by captured forms deployed in Indonesia, China, and North Korea. Indonesian types saw service into its war with the Dutch during its fight for independence and many were lost as a result. Chinese Ki-51s lasted until 1953 in service. North Korean mounts were made available through the Soviet Union immediately after the war, helping to build up the North's air power.

Any available statistics for the Mitsubishi Ki-51 (Sonia) Ground Attack / Reconnaissance Aircraft are showcased in the areas immediately below. Categories include basic specifications covering country-of-origin, operational status, manufacture(s) and total quantitative production. Other qualities showcased are related to structural values (namely dimensions), installed power and standard day performance figures, installed or proposed armament and mission equipment (if any), global users (from A-to-Z) and series model variants (if any).

Our Data Modules allow for quick visual reference when comparing a single entry against contemporary designs. Areas covered include general ratings, speed assessments, and relative ranges based on distances between major cities.

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Relative Maximum Speed Rating
Hi: 300mph
Lo: 150mph
    This entry's maximum listed speed (264mph).

    Graph average of 225 miles-per-hour.
Relative Operational Ranges
Graph showcases the Mitsubishi Ki-51 (Sonia)'s operational range (on internal fuel) when compared to distances between major cities.
Aviation Era Impact
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Useful in showcasing the era cross-over of particular aircraft/aerospace designs.
Unit Production Comparison
Comm. Market HI*: 44,000 units
Military Market HI**: 36,183 units

  * Commercial Market High belongs to Cessna 172.

  ** Military Market High belongs to Ilyushin Il-2.

Altitude Visualization
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Mitsubishi Ki-51 (Sonia) Specifications
National Flag Graphic
Imperial Japan
Year: 1940
Type: Ground Attack / Reconnaissance Aircraft
Manufacturer(s): Mitsubishi / Tachikawa Army Air Arsenal - Imperial Japan
Production: 2,385
Supported Mission Types
Ground Attack
Close-Air Support
Airborne Early Warning
Electronic Warfare
Aerial Tanker
Passenger Industry
VIP Travel
Business Travel
Special Forces
Crew: 2
Length: 30.18 ft (9.2 m)
Width: 39.70 ft (12.10 m)
Height: 8.96 ft (2.73 m)
Empty Weight: 4,129 lb (1,873 kg)
MTOW: 6,437 lb (2,920 kg)

Installed Power
1 x Mitsubishi Ha-26-II radial piston engine developing 940 horsepower.

Standard Day Performance
Maximum Speed: 264 mph (425 kph; 229 kts)
Maximum Range: 659 mi (1,060 km; 572 nm)
Service Ceiling: 27,133 ft (8,270 m; 5.14 mi)
Rate-of-Climb: 1,640 ft/min (500 m/min)

2 x 7.7mm Type 89 machine guns in wings
1 x 7.7mm Te-4 machine gun on trainable mount in rear cockpit.

2 x 12.7mm heavy machine guns in wings
1 x 7.7mm Te-4 machine gun on trainable mount in rear cockpit.

Up to 440lbs of external stores (550lbs in kamikaze role).

Operators List
Imperial Japan

Series Model Variants
• Ki-51 (prototype) - 2 example prototypes completed for testing and evaluation; a further 11 were completed for service trials.
• Ki-51-I - Initial production model; 2,372 examples completed.
• Ki-71 - Proposed tactical reconnaissance variant by Mansyu; retractable undercarriage; 3 prototypes completed; no serial production ordered.

Supported Weapon Systems
Graphical image of an aircraft medium machine gun
Graphical image of an aircraft heavy machine gun