The Kawasaki Ki-48 was a nicely designed aircraft, fast, manoeuvrable, and well armed both offensively and defensively-for its time, which was the late 1930s and up through early 1942. Then, the changing pattern of the air war over the Pacific-Asian battlefronts, and the changing operational requirements, left this trim little twin-engined light bomber behind. Although its production ended in October 1944 with 1,977 examples built, it remained in service because, by that date, Japan was plainly losing the war, and was in dire need of virtually anything that could fly-particularly for "special" (suicide) attacks.

Early in the Sino-Japanese War of 1937, China deployed numbers of Russian-built Tupolev SB-2 light bombers, sometimes crewed by Soviets, on hit-and-run attacks against the Japanese invaders. The Japanese were surprised by this aircraft's speed; it was faster than the Ki-10 biplane fighter, and was nearly as fast as the Ki-27 monoplane fighter which was just entering service with the Japanese Army Air Force. Certain air staff officers were so impressed by the SB-2's performance that they obtained the go-ahead to begin development of a similar light bomber for the JAAF. Kawasaki Aircraft Ltd. was issued the specifications in December 1937. These called for a twin-engined light bomber with (a) a top speed of 298 mph at 9,845 feet; (b) a cruising speed at the same altitude of 217 mph; (c) climb to 16,405 feet in 10 minutes; (d) a bombload of 882 pounds; (e) engines to be Nakajima Ha-25 radials; (f) defensive armament of three or four flexible 7.7mm machine guns; and (g) ability to operate under the extreme winter conditions prevailing in Manchuria and North China.

Actual design work began in January 1938 with Dr. Takeo Doi in charge, but because he was also in charge of the Ki-45 twin-engined fighter design team, and the Ki-45 had a higher priority, the first prototype of the new light bomber wasn't ready for flight until more than a year and a half passed, in July 1939. Experience gained from designing the Ki-45 was incorporated into the bomber project. The cantilever wing was mid-mounted to allow an internal bomb bay. The crew of four was to consist of the pilot, a bombardier/nose gunner with a 7.7mm weapon at his disposal, a radio-operator/gunner manning the dorsal 7.7mm machine gun, and a navigator/gunner utilizing the ventral 7.7mm gun. Normal bombload was to be twenty-four 33-lb. bombs or six 110-lb. bombs, and the twin engines were, as per the requirements, Nakajima Ha-25s driving three-bladed variable-pitch propellers.

Ki-48 parked at a forward airfield in either China or the Philippines, 1944.

During the prototype's flight trials, it easily met all performance requirements and won praise from Army test pilots for its manoeuvrability and handling characteristics, but it suffered from severe tail flutter. Five further prototypes, built between September and November of 1939, tested various tail-surface modifications, until it was found that raising the horizontal stabilizers approximately 13 ¾ inches and generally strengthening the rear fuselage was the combined solution to the flutter problem. Very late in 1939, quantity production of the new light bomber commenced under the designation Army Type 99 Twin-Engined Light Bomber Model 1A, or Ki-48-Ia.

The first production Ki-48-Ia was completed in July of the next year, and by that autumn, the 45th Sentai (Group) was re-equipped with the new aircraft and deployed to the North China battlefront, where the Ki-48 swiftly won a high reputation with its crews. Facing largely token Chinese opposition, the Ki-48 performed satisfactorily, winning much praise for its high speed. In addition to daylight tactical sorties, night strategic attacks were pioneered by the 45th Sentai, in preparation for similar attacks on the forces of the Western Allies in the upcoming Pacific War. Late production Ki-48-Is were designated Ki-48-Ib, differing from the earlier model solely in having minor internal equipment changes and improved machine gun mountings.

When the Pacific War began, the Ki-48 was the most important JAAF light bomber outside the Chinese front; the older single-engined Ki-30 and Ki-32 were retained for China service. Aircraft of the 8th, 27th, 75th, and 90th Sentais were deployed against Commonwealth forces in Malaya and Burma, and against the Americans in the Philippines, before being transferred to the Dutch East Indies, and later to New Guinea. But against Allied fighters of more modern vintage, the Ki-48-I fared badly; the high turn of speed it was so praised for over China was too low to allow the Lily, as the Allies code-named it, to avoid interceptors. Also, its defensive armament was wholly inadequate, its bomb load was too small, and it lacked any form of crew or fuel-tank protection. To limit combat losses, the early model Lilies were used for night attacks whenever possible, reducing their effectiveness even more.

Close-up of the Ki-48's ventral gun position.

An improved model of the Lily was already being developed as the Pacific War commenced. The Ki-48-II differed little from its predecessor, but it incorporated a slightly lengthened fuselage, improved engines (Nakajima Ha-115s with a two-stage blower), some fuel-tank protection, and some armour for the crew, including a 12.5mm plate behind the bombardier's seat, a 6.5mm plate under the pilot's seat, 16.5mm armour behind the pilot's seat, and 16.5mm plates to protect the dorsal and ventral ammunition boxes. Within two months of its first flight, the Ki-48-II entered production as the Ki-48-IIa. These production planes differed from the prototypes only in minor details, such as local strengthening of the fuselage. The Ki-48-IIb was a dive bomber, fitted with retractable dive brakes under the outer wings (these were of the "snow-fence" variety).

The maximum bomb-load of the Ki-48-II was double that of the -I, but it was still a great deal less than that of the standard Allied light bomber, the A-20 Havoc. And although the speed of the Ki-48-II was superior to that of the -I, it was still not fast enough to outrun the improved Allied fighters of the later-war period. But its worst failing was its woefully inadequate defensive armament, which had not been improved since the prototype first flew. The Lily proved to be "easy meat" in the air, and large numbers were also destroyed on the ground in New Guinea despite Japanese efforts to disperse and camouflage the planes on their jungle airstrips.  

An attempt to fit a single example of the Lily with a 20mm cannon in a revolving turret was unsuccessful due to the increased weight and the complication of such a fitting on a plane as small as the Ki-48. The final production variant, the Ki-48-IIc, received a 12.7mm machine gun in a flexible dorsal mounting, plus a second nose-mounted 7.7mm machine gun; the bombardier could use either gun as needed. Still, despite all attempts to keep the Ki-48 a viable warplane, it was obvious the type was obsolescent, and so production ended in the autumn of 1944, as noted above. Some Ki-48-IIs continued to serve in a conventional bombing role, mainly at night, in the Philippine and Okinawan campaigns. But most surviving Lilies were expended in daylight suicide attacks in the latter campaign, usually en masse, in the Kikusui (Floating Chrysanthemum) raids. A number of Ki-48-IIs were modified as Ki-48-II-KAI special attack planes by the Army Air Arsenal at Tachikawa. These carried a 1,764-lb. bombload, triggered upon contact with the target by means of a long rod protruding from the aircraft's nose like a mosquito's proboscis.

Ki-48 abandoned in the Philippines, 1945.

Four Ki-48-IIbs were used in 1944 to test the Kawasaki I-Go-I-B air-to-surface guided missile, and another Ki-48-II was used to test the experimental Ne-O turbojet in flight; to accomplish this, the bomb-bay doors were removed and the jet engine was slung under the fuselage. In addition, two proposed but never-built variants were the Ki-81 formation commander's aircraft, heavily armed and armoured; and a single-seat special attack aircraft, the Ki-174.