The Kawasaki Ki-48 Army Type 99 Twin-engined Light Bomber (Lily) was a fast but under-armed light bomber that performed well over China in 1940 but proved to be vulnerable when faced with more modern Allied fighters.
The Ki-48 was inspired by the Soviet Tupolev SB-2, a fast bomber that had served against the Japanese in the Second Sino-Japanese War, and had proved to be almost impossible to intercept, with a top speed close to that of the newest Japanese army fighter, the Nakajima Ki-27.
In December 1937 the Japanese Army instructed Kawasaki to begin development of an aircraft with a top speed of 298mph at 9,845ft, a cruising speed of 217mph, a payload of 882lb (400kg), armed with three or four flexibly mounted 7.7mm machine guns and capable of operating in extreme cold weather. The new aircraft was to be powered by two Nakajima Ha-25 radial engines.
The new aircraft was designed by a team led by Takeo Doi, who was also working on the Ki-45 Toryu. Work began in January 1938, and the first prototype was completed in July 1939. The new aircraft reached all of its performance targets, but suffered from severe tail flutter, which required five pre-production aircraft to solve. Late in 1939 these problems were solved, and the Ki-48 was ordered into production as the Army Type 99 Twin-engined Bomber Model 1A.
The resulting aircraft was very similar in appearance to twin-engined bombers produced elsewhere in the world, with a glazed nose and a raised main cabin, with glazed pilot's canopy and a glazed rear canopy. Initial versions were armed with three flexibly mounted 7.7mm machine guns, one in the nose and one each in rear-firing dorsal and ventral positions.
The Ki-48-I made its combat debut in China in the autumn of 1940, and lived up to expectations, proving to be almost immune to interception. Unfortunately this would soon prove to have had more to do with the weakness of the Chinese air force than the strengths of the Ki-48.
The Ki-48-I proved to be rather vulnerable when it came up against Commonwealth and American fighter aircraft early in the Pacific War. Its speed wasn't high enough to avoid enemy fighters, its defensive firepower insufficient to fight them off, and its lack of armour and self-sealing fuel tanks made it vulnerable when it was caught.
An improved version of the aircraft was already under development. The Ki-48-II or Army Type 99 Twin-Engined Light Bomber Model 2 had armour around the fuel tanks, and 6.5-16.5mm of armour protecting the crew. Power was provided by two Nakajima Ha-115 engines, with a two-stage blower that improved higher altitude performance and a normal rating of 1,150hp (compared to 950hp on the Ki-48-I). The Ki-48-II had a top speed of 314mph at 18,375ft, a significant improvement on the 298mph at 11,485ft of the Ki-48-I. Normal payload also increased by 25%, from 661lb (300kg) to 882lb (400kg), while the maximum payload doubled, to 800kg (1,764lb). Only the defensive firepower failed to improve, at least until the appearance of the Ki-48-IIc, which carried a second 7.7mm gun in the nose and a 12.6mm in the dorsal position.
Despite these improvements the Ki-48-II was still very vulnerable during daylight operations. They were used at great cost during the fighting over the Philippines, but retreated to night time operations over Okinawa, before the surviving aircraft were used on suicide missions.
A small number of aircraft were modified to carry a 1,764lb bomb-load, triggered by a long rod mounted in the nose, as the Army Type 99 Special Attack Plane (Ki-48-II KAI). A purpose-built suicide version of the aircraft, the single seat Ki-174, never reached production.
Ki-48 was the designation given to four prototypes and to five pre-production aircraft that were used to solve problems with tail flutter, eventually fixed by raising the horizontal tail surfaces by 13 3/4in and strengthening the tail.
The Ki-48-Ia (Army Type 99 Twin-engined Light Bomber Model 1A) was the first production version of the aircraft. It was based on the final version of the pre-production aircraft, and was armed with three 7.7mm guns, in the nose, dorsal and ventral positions. The Ki-48-Ia had a normal bomb load of 661lb and a maximum bomb load of 882lb.
The Ki-48-Ib was a minor improvement, with new gun mountings and minor equipment changes. A total of 557 Ias and Ibs were built before production switched to the Ki-48-II after June 1942.
The Ki-48-II was the designation given to three prototypes with the Nakajima Ha-115 engine, completed in February 1942. The Ki-48-II was externally very similar to the Ki-48-I, although with a slight increase in length. The normal payload increased to 882lb and the maximum to 1,764lb.
The Ki-48-IIa (Army Type 99 Light Bomber Model 2A) was the initial production version of the Ki-48-II, and was placed into production in April 1942. The Ki-48-IIa was very similar to the prototypes, although with a stronger fuselage in places.
The Ki-48-IIb (Army Type 99 Light Bomber Model 2B) was given dive-breaks carried under the outboard wing panels.
The Ki-48-IIc (Army Type 99 Light Bomber Model 2C) an up-armed version of the aircraft, with two 7.7mm machine guns in the nose, one in the ventral position and a 12.7mm gun in the dorsal position. It entered production in 1943, but didn't solve the type's lack of defensive firepower. Production ended in October 1944 after 1,408 Ki-48-IIs had been built.
Engine: Two Army Type 99/ Nakajima Ha-25 air-cooled radial engines
Power: 950hp (1,000hp at take-off, 980 at 9,845ft)
Wing span: 57ft 3in (17.47m)
Length: 41ft 4in (12.6m)
Height: 12ft 5in (3.8m)
Empty Weight: 8,929lb
Loaded Weight: 13,007lb
Max Speed: 298mph at 11,485ft
Cruising Speed: 217mph
Service Ceiling: 31,170ft
Range: 1,230 miles
Armament: Three 7.7mm machine guns
Bomb-load: 661lb normal, 882lb maximum
Engine: Two Army Type I/ Nakajima Ha-115 air-cooled radial engines
Power: 1,150hp (1,130hp at take-off, 1,070hp at 9,185ft, 950hp at 18,375ft)
Wing span: 58ft 3in
Length: 41ft 9in (12.75m)
Height: 12ft 5in (3.8m)
Empty Weight: 10,031lb
Loaded Weight: 14,330lb
Maximum Weight: 14,81lb
Max Speed: 314mph at 18,375ft
Service Ceiling: 33,135ft
Range: 1,274 miles
Armament: Three 7.7mm machine guns
Bomb-load: 882lb normal, 1,764lb maximum