The Mitsubishi Ki-51 Type 99 Assault Plane (Allied codename: Sonia) was a military attack aircraft used during World War II by the Imperial Japanese Army Air Force. The first production model of the Ki-51 series was the Ki-51-I model which had a single Mitsubishi Ha-26 engine which was capable of propelling it at speeds of up to 423 kilometers per hour. However, the top speed of the aircraft was affected by the non retractable landing gear.