The Mitsubishi Ki-1 Army Type 93 Heavy Bomber was an unsuccessful attempt to produce a heavy bomber based on the Junkers K 37, and was an unpopular aircraft in service.
In February 1931 a group of private sponsors purchased a Junkers K 37 bomber (produced by Swedish-Junkers) and donated it to the Japanese Army as Aikoku No.1 (Patriotic Gift No.1). This aircraft was tested in combat in Manchuria, where its performance convinced the Japanese army to order production of a similar aircraft.
Mitsubishi first became involved with Junkers in 1928 when work began on turning the Junkers G 38 four engined passenger aircraft into the Ki-20 Army Type 92 Heavy Bomber. The first of these aircraft was completed in 1931 and this experience may have played a part in Mitsubishi being awarded the contract to produce a heavy bomber based on the K 37 in April 1932 (In September they were also asked to produce a light bomber based on the same K 37, which became the Ki-2).
The Army provided Mitsubishi with clear specifications. It was to be a twin-engined monoplane, powered by two 800hp engines but with the ability to fly on one engine. Normal bomb load was to be 2,200lb with a maximum bomb load with reduced fuel of 3,300lb. It was to operate between 3,280 and 6,560ft and have a top speed of 150mph. Three 7.7mm machine guns were to be carried. Two prototypes were ordered, to be complete by the end of March 1933.
Mitsubishi responded with an enlarged version of the K 37 (the Ki-2 would be about the same size as the original K 37). The chief designer on the project was Nobushiro Nakata, who had performed the same role on the Ki-20.
The Ki-1 was a cantilever low-wing aircraft, with a fixed undercarriage and the standard Junkers corrugated skin. The two pilots sat in tandem in a cockpit above the wing. There was also a position for a bombardier/ nose gunner in the nose and an open cockpit for the dorsal gunner.
The first mock-up was ready in August 1932 and the prototype was completed on time in March 1933. It was powered by two 800hp Rolls-Royce Buzzard engines, the Mitsubishi Type 93 engine having been delayed. The prototype was 12mph slower than expected, and couldn't fly on a single engine. Despite these problems the type was accepted for production as the Army Type 93 Heavy Bomber (this version was later re-designated as the Army Type 93-1 Heavy Bomber or the Ki-1-I).
A total of 118 aircraft were built between 1933 and 1936. Most of these were Ki-1-Is, but later aircraft were completed as the improved Ki-1-II (Army Type 93-2 Heavy Bomber). These aircraft had a longer cockpit canopy that covered the dorsal gunner's position, lower mounted engines and smooth instead of corrugated panels on the wings.
The Ki-1 was used in combat in Manchuria and northern China, but was not considered to be a success. The Army airmen preferred the Mitsubishi Ki-2 Type 93 Twin-engined Light Bomber, which was more manoeuvrable and faster.
In 1936 the Japanese Army issued the specifications that led to the Ki-21 Type 97 Heavy Bomber (Sally), and at the same time they purchased 100 Fiat BR.20 bombers, which briefly replaced the Ki-1 in service, as the Type I Heavy Bomber.
Engine: Two Type 93 (Ha-2II) twelve cylinder vee water cooled engines
Crew: 4 (two pilots, Bombardier/ nose gunner, dorsal gunner)
Span: 86ft 11.5in
Length: 48ft 6.5in
Height: 16ft 2in
Empty weight: 10,758lb
Loaded weight: 17,857lb
Max speed: 137mph
Climb Rate: 14 minutes to 9,843ft
Service ceiling: 16,404ft
Armament: Three flexibly mounted 7.7mm machine guns - one nose mounted, one dorsal mounted, one ventral mounted
Bomb load: 2,204.5lb standard, 3,306.8lb maximum