Mitsubishi Type 99 Reconnaissance Plane Guntei / Ki-51A (Sonia)
Mitsubishi Type 99 Assault Plane Shugeki / Ki-51B (Sonia)
Technical Information

Background
The Mitsubishi Type 99 Reconnaissance Plane / Assault Plane was a single engine aircraft with fixed landing gear with a pilot and observer. Used by the Japanese Army Air Force (JAAF) for reconnaissance and assault missions. Armed with two 7.7mm machine guns in the wings and one flexible 7.7mm machine gun in the rear canopy plus a wing mounted bomb load. This aircraft was well regarded by pilots and ground crews because it was easy to fly, maintain, and operate from small forward airfields.

Reconnaissance Version (Guntei, Ki-51A)
(Kyu Kyu Shiki Gun Teisatsu Ki) Reconnaissance version. Production ended during November 1941. The 83rd Independent Air Chutai operated the Ki-51A Sonia in China until April 1943 at Luisu Airfield then transfered to the South Seas Area, operating from Wewak Central Airfield using Madang Airfield as a forward operating base and operated from Lae Airfield during the middle of May 1943 until the the Allied liberation of Lae.

Assault Version (Ki-51B)
(Kyu Kyu Shiki Shuugeki Ki) Also known as Shugeki or Shuhgeki. The assault version had armor plating protecting the pilot and oil tanks, and bomb racks to carry 441 pounds of bombs. This version could be modified in the field to carry an aerial camera. The 26th Flying Regiment operated the Ki-51B Sonia in New Guinea.

Production
A total of 2,388 were built, by two factories: Mitsubishi and the 1st Army Air Arsenal
Mitsubishi produced a total of 1,472.
1st Army Air Arsenal produced a total of 913.

References
Production Record of the Type 99 Assault / Recon Plane by Jim Long
Advance Echekon FEAF Tokyo "Monthly Production Figures on aircraft, engines & propellers" October 26, 1945 page 6
軍偵部隊の足跡 / Guntei Butai No Ashiato: Dokuritsu Hiko Dai 83 Chutai Shi - "Footsteps of a Tac Reconn Unit: History of the 83rd Independent Flying Chutai 1988
Thanks to Nicholas Millman and Richard Dunn for additional information

Technical Details (Ki-51B)
Crew  Two (pilot, observer)
Engine  1 x Mitsubishi Ha-26-II 14-cylinder air-cooled radial piston engine 710 kW (950 hp) with 3 bladed propeller
Span  12.1m
Length  9.21m
Height  2.73m
Maximum Speed  263 mph
Range  660 miles
Armament  (wings) 2 x 12.7mm MG (rear) 1 x 7.7mm MG
Bomb Load  441 pounds