For most of the air forces of the major fighting powers the fast twin-engined medium bomber was an all-important weapon. Japan, however, did not possess an equivalent aircraft until 1944 when the Japanese Army introduced their Ki-67 Hiryu, and the Navy took delivery of their P1Y1 Ginga (Milky Way). The prototype of this aircraft had made its first flight in the summer of 1943, and confidence in its performance was so high that Nakajima, the prime producer, went directly from prototype manufacture to quantity production. Including the prototypes, forty-five P1Y1s were delivered in 1943, and monthly output increased steadily, a total of 453 P1Y1s being built by the time the aircraft was finally accepted by the Navy in October 1944. Unfortunately for Japan the serviceability and reliability of the Ginga were not very satisfactory, and for a while the Navy found themselves with a large number of aircraft not yet accepted for Service use.
The development of the P1Y series was initiated by Kugisho (an WW II acronym for Dai-Ichi Kaigun Koku Gijitsusho, First Naval Air Technical Arsenal). Kugisho was based at Yokosuka, hence the type is often incorrectly designated Yokosuka P1Y Ginga. The type was designed to meet the requirements of a 15-Shi (1940) specification calling for a fast bomber capable of undertaking low-altitude attacks as well as torpedo and dive-bombing attacks. The intention was to produce an aircraft comparable to the Junkers Ju 88, North American B-25 and Martin B-26. To that effect, an engineering team led by Tadanao Mitsuzi and Masao Yamana designed an extremely clean twin-engined aircraft with a narrow circular fuselage with mid-mounted wings.
The power plant selected was the Nakajima Homare radial then still in the design stage. With a pair of these engines the P1Y was expected to reach a top speed of over 345 mph (555 kmh) and in spite of its small size, provision was made in the wings for eight protected and six unprotected fuel tanks with a total capacity of 1,462.19 gal (5,535 l) to which could be added two 58.11 gal (220 l) drop tanks. Two oil tanks were mounted in each engine nacelle, but armor protection was restricted to a 0.787 in (20 mm) plate behind the pilot's head. Compared with contemporary Allied aircraft, the defensive armament, limited to a single flexibly mounted machine gun in the nose and rear cockpit positions, was utterly inadequate and the aircraft was to rely on its speed to avoid interception. Normal offensive load was to consist of either a single 1,764 lb (800 kg) torpedo carried semi-internally under the fuselage or two 1,102 lb (500 kg) bombs carried in a ventral bomb-bay.
While detailed design work on the aircraft, then known as the Y-20, was progressing at Kugisho, the Navy decided to assign its manufacture to Nakajima's Koizumi plant (some 40 mls, 64 km north of Tokyo), where production of the Mitsubishi G3M ("Nell") was scheduled to terminate in early 1943. In February 1943 the last five G3M3s were rolled out at Koizumi and the assembly lines quickly dismantled to make room for the P1Y production line.
Powered by a pair of Nakajima Homare 11 radials, the first prototype was completed in August 1943 and made its maiden flight shortly after. Its high speed and ease of handling were soon commented upon favorably by the manufacturer's pilots and Service pilots, but their enthusiasm was not shared by the ground crews who were experiencing considerable difficulties with its troublesome hydraulic system and unreliable power plants. Even under the most favorable conditions obtained during the flight trials program, when the manufacturer's experienced mechanics were available at all times, maintenance problems caused numerous difficulties and, although production was rapidly growing, for over a year the Navy delayed acceptance of the P1Y1 for Service use.
During that period numerous changes were introduced on the assembly lines, the first of these consisting of replacing the curved windshield with a new unit incorporating a flat bullet-proof panel, the installation of a revised cowling with individual exhaust stacks instead of a single exhaust pipe, and in using flat-headed rivets in place of the original flush rivets on the fuselage. Production aircraft also differed from the prototypes in being powered by Homare 12 radials and in the fitting of a fixed tail wheel instead of the retractable one. Numerous changes were also incorporated in the defensive armament, and initial production aircraft mounted a flexible cannon in the nose in place of the prototypes' machine gun, and, when production allowed, the slow-firing Type 99 Model 1 cannon in the nose and dorsal positions were replaced by Type 2 machine guns on single or twin mountings (P1Y1a, P1Y1b and P1Y1c). Late production aircraft were also fitted with air-to-sea search radar, and it was also planned to use the P1Y1 as a parent aircraft for the Ohka Model 22 suicide aircraft.
Finally the Navy accepted the aircraft for Service use, and the P1Y1 became known as the Navy Bomber Ginga Model 11. Unrelenting maintenance problems, notably resulting from the unreliable Homare 12 engine, which seldom delivered its rated power, still kept the aircraft from combat until the early part of spring 1945. However, when the Ginga was finally committed to combat operations, it justified the Navy's most optimistic hopes, and although it was only in combat for less than six months, "Frances", as the Allies named this new foe, was a most respected aircraft.
During its flight trial program the P1Y1 with its maximum speed of 340 mph (547 kmh) had attracted the attention of the naval pilots who were attempting to create a night fighting force against expected Allied night bombing operations over the Japanese mainland. To meet this requirement the Navy instructed Kawanishi to produce in their Konan plant a night fighter version of the P1Y1. As it was feared that Homare engine production would be insufficient to meet all demands, Kawanishi decided to install a pair of Mitsubishi Kasei 25a radials on the night fighter. Designated P1Y2-S, the Kawanishi-built aircraft retained the ventral bomb-bay, as they were intended to be operated as night intruders as well as night fighters. The machine gun in the nose of the bomber was eliminated on the P1Y2-S, but a pair of Type 99 Model 2 cannon were mounted obliquely in the fuselage to fire up and forwards, and the flexibly mounted Type 99 cannon in the rear cockpit was retained.
First flown in June 1944, the P1Y2-S went into production as the Navy Night Fighter Kyokko (Aurora), but its performance at altitude proved somewhat disappointing. As a result on most of the ninety-six P1Y2-S built the angled machine guns were removed, and these aircraft were operated as bombers under the designation Navy Bomber Ginga Model 16 (P1Y2). A modification of the Nakajima-built P1Y1, the Navy Night Fighter Byakko (White Light) (P1Y1-S), fitted with two pairs of obliquely-mounted cannon - one forward and the other aft of the cockpit - proved equally unsuccessful. Numerous modifications of the P1Y series were made during the last year of the war, and these included the fitting of wooden tail surfaces and rear fuselage sections on a limited number of aircraft, and the experimental testing of a power-operated dorsal turret, mounting two cannon. The third prototype was used to test-fly the Tsu-11 Campini-type jet engine intended for the Ohka Model 22 series, while one aircraft was also tested with ten forward-firing cannon.
A total of 1,098 P1Ys were produced, Nakajima Hikoki K.K. at Koizumi built the six prototypes in 1943, till 1945 followed by 996 P1Y1 and P1Y1-S, while Kawanishi Kokuki K.K. at Konan built 96 P1Y2 and P1Y2-S in 1944-1945.
Description
Twin-engined medium bomber, designated P1Y1 and P1Y2, or night fighter, designated P1Y1-S and P1Y2-S. All were of all-metal construction, with crew of three in enclosed cockpits.
Power plant
Prototypes and P1Y1: Two Nakajima NK9B Homare 11 eighteen-cylinder air-cooled radials rated at 1,820 hp for take off, 1,650 hp at 6,560 ft (2,000 m) and 1,440 hp at 18,700 ft (5,700 m), driving three-blade pro-pellers.
P1Y1a, P1Y1b, P1Y1c and P1Y1-S: Two Nakajima NK9C Homare 12 eighteen-cylinder air-cooled radials rated at 1,825 hp for take off, 1,670 hp at 7,875 ft (2,400 m) and 1,500 hp at 21,655 ft (6,600 m), driving three-blade propellers.
P1Y2 and P1Y2-S: Two Mitsubishi MK4T-A Kasei 25a fourteen-cylinder air-cooled radials rated at 1,850 hp for take off, 1,680 hp at 8,530 ft (2,600 m) and 1,540 hp at 18,045 ft (5,500 m), driving three-blade propellers.
Armament
Prototypes: One flexible 0.303 in (7.7 mm) Type 92 machine gun in the nose and one flexible rear-firing 0.787 in (20 mm) Type 99 cannon.
P1Y1 (experimental installation on one aircraft): Ten forward-firing 0.787 in (20 mm) Type 99 cannon and one flexible rear-firing 0.511 in (13 mm) Type 2 machine gun.
P1Y1 and P1Y2: One flexible 0.787 in (20 mm) Type 99 cannon in the nose and one flexible rear-firing 0.787 in (20 mm) Type 99 cannon.
P1Y1a and P1Y2a: One flexible 0.787 in (20 mm) Type 99 cannon in the nose and one flexible rear-firing 0.511 in (13 mm) Type 2 machine gun.
P1Y1b and P1Y2b: One flexible 0.787 in (20 mm) Type 99 cannon in the nose and twin 0.511 in (13 mm) Type 2 machine guns in a dorsal turret.
P1Y1c and P1Y2c: One flexible 0.511 in (13 mm) Type 2 machine gun in the nose and twin 0.511 in (13 mm) Type 2 machine guns in a dorsal turret.
P1Y2-S: One flexible rear-firing 0.787 in (20 mm) Type 99 cannon and two oblique-firing 0.787 in (20 mm) Type 99 cannon.
P1Y1 and P1Y2 bomb-load: one 1,764 lb (800 kg) torpedo or up to 2,205 lb (1,000 kg) of bombs.
Specifications
A
Span:
Length:
Height:
Wing area:
Empty weight:
Loaded weight:
Max weight:
Wing loading:
Power loading:
Max speed:
Cruise speed:
Climb:
Service ceiling:
Range:
P1Y1
65 ft 7.4 in (20.00 m)
49 ft 2.55 in (15.00 m)
14 ft 1.3 in (4.30 m)
592 sq.ft (15.00 sq.m)
16,017 lb (7,265 kg)
23,149 lb (10,500 kg)
29,762 lb (13,500 kg)
39.1 lb/sq.ft (190.90 kg/sq.m)
8.2 lb/hp (2.90 kg/hp)
340 mph (547 kmh) at 19,355 ft (5,900 m)
230 mph (370 kmh) at 13,125 ft (4,000 m)
to 9,843 ft (3,000 m) 4 min 15 sec
30,840 ft (9,400 m)
3,337 mls (5,370 km)
P1Y2-S
65 ft 7.4 in (20.00 m)
49 ft 2.55 in (15.00 m)
14 ft 1.3 in (4.30 m)
592 sq.ft (15.00 sq.m)
17,196 lb (7,800 kg)
23,149 lb (10,500 kg)
29,762 lb (13,500 kg)
39.1 lb/sq.ft (190.90 kg/sq.m)
8.2 lb/hp (2.90 kg/hp)
325 mph (523 kmh) at 17,715 ft (5,400 m)
230 mph (370 kmh) at 13,125 ft (4,000 m)
to 16,405 ft (5,000 m) 9 min 2 sec
31,365 ft (9,560 m)
2,476 mls (3,985 km)