The Yokosuka P1Y Ginga (Milky War) 'Frances' was a promising twin-engined medium bomber let down by reliability problems. These delayed its service entry until 1945, five years after work began on the aircraft.
Work on the P1Y began in 1940 in response to a 15-Shi specification for a fast low-altitude bomber that could also serve as a torpedo bomber or a dive bomber. The P1Y was designed by a team led by Tadanao Mitsuzi and Masao Yamana, based at the Naval Arsenal at Yokosuka.
They produced an elegant twin-engined aircraft. It has a narrow circular fuselage, with straight edged tapered mid-mounted wings. It has a glazed nose and a greenhouse canopy over the main cockpit, which was mounted just above the wings.
The designers decided to use the new Nakajima Homare eighteen cylinder air-cooled radial engine. This engine was still under development at the time, and as in so many cases this proved to be a mistake, with the aircraft's reliability dragged down by the untested engines.
The P1Y was armed with two flexibly mounted machine guns. It could carry one 1,764 torpedo carried partly recessed into the bomb bay or two 1,102lb bombs within the bomb bay. There were 14 fuel tanks in the wings - eight of them protected and six unprotected. These allowed the aircraft to carry 1,218 imperial gallons of fuel, with another 96 in drop tanks. As was so often the case with Japanese aircraft, it was almost entirely un-armoured, although there was a 20mm sheet of armour behind the pilot's head.
Great things were expected of the P1Y, even before it had made its maiden flight. In February 1943 work began on building a production line for the new aircraft at the Nakajima Koizumi factory.
The prototype P1Y, powered by two 1,820hp Homare engines, made its maiden flight in August 1943. The aircraft quickly proved to have two sides to its characters. The ground crews encountered problems with the new engines and with the hydraulics. The P1Y was an advanced design that needed careful maintenance, but even the Yokosuka mechanics struggled to keep the prototype running. In the air the picture was much better. The P1Y was fast and handled well and was popular with its pilots.
For some time the reliability problems won out. Yokosuka and Nakajima produced 45 aircraft in 1943 and a total of 453 before the Japanese Navy finally accepted the aircraft for service in October 1944. During this time a series of changes were made to the design. A flat bullet-proof windscreen was installed. A new engine cowling with individual exhaust stacks replaced the original model with a single exhaust pipe.
The defensive armament was improved - the prototype had been armed with a flexibly mounted 7.7mm machine gun in the nose and a slow-firing 20mm cannon in the rear. Early production aircraft had a 20mm cannon in the nose. The rear firing 20mm cannon was then replaced with a 13mm Type 2 machine gun. Later machines got a twin 13mm machine gun dorsal turret and some also has the nose cannon replaced by a 13mm machine gun. The faster rate of fire of the 13mm gun more than made up for the decrease in shell size.
The P1Y Navy Bomber Ginga (Milky Way) was finally ready to enter combat in the spring of 1945. Despite its long development process the aircraft was still impressive, and it could outrun most Allied fighters at low level. Despite the best efforts of Nakajima and Yokosuka it was still rather difficult to maintain, and suffered from low serviceability levels. This was made worse by the increasing shortage of skilled mechanics by 1945, with many killed in action earlier in the war.
The P1Y was also used as the basis for two fighter variants. The P1Y1-S Navy Night Fighter Byakko (White Light) was based on Nakajima production aircraft. The P1Y2-S Kyokko (Aurora) was custom built by Kawanishi, using two Mitsubishi Kasei 25a fourteen-cylinder radial engines. The Kyokko was armed with two obliquely mounted 20mm cannon and kept the rear-firing cannon. High altitude performance was poor, and most were converted back into bombers, becoming the P1Y2 Navy Bomber Ginga Model 16.
Eventually 1,098 P1Ys were built. Six prototypes were built in 1943. Nakajima produced 996 P1Y1s and P1Y1-Ss during 1943-45. Kawanishi produced 96 aircraft, starting with the P1Y2-S but converting them to the P1Y2 bomber later.
P1Y1 Navy Bomber Ginga Model 11
The P1Y1 was the main production version of the aircraft. It was powered by the Nakajima Homare engine, with the basic P1Y1 using the 1,820hp Homare 11 and the sub-variants using the 1,825hp Homare 12, which retained more power at higher altitude.
The basic P1Y1 was armed with one flexibly mounted 20mm Type 99 cannon in the nose and one flexibly mounted rear-firing 20mm Type 99 cannon.
The P1Y1a replaced the rear-firing cannon with a faster firing 13mm Type 2 machine gun. It kept the 20mm cannon in the nose.
The P1Y1b kept the nose cannon, but replaced the single 13mm Type 2 machine gun with two 13mm machine guns in a dorsal turret.
The P1Y1c replaced the nose cannon with a 13mm Type 2 machine gun and retained the two gun dorsal turret.
P1Y2 Navy Bomber Ginga Model 16
The P1Y2 was the designation given to those P1Y2-S Kyokko night fighters that were converted back to the bomber role by removing the obliquely mounted guns. They then differed from the P1Y1 by using Mitsubishi engines instead of the normal Homare engines. The P1Y2 had the same armament variants as the P1Y1.
P1Y3 Model 33
The P1Y3 was to have been a mother-ship for the Ohka jet or rocket powered suicide aircraft. It was to have a wider wingspan and longer fuselage so that it could cope with the extra weight and size of the Ohka. It never got beyond the drawing board stage.
P1Y4 Model 12
The P1Y4 was a design for a version of the standard aircraft that would have been powered by two 2,000hp Homare radial engines.
P1Y5 Model 14
The P1Y5 would have been powered by two 2,200hp Mitsubishi MK9A radial engines
P1Y6 Model 17
The P1Y6 would have been powered by the Kasei 25c engine and built by Kawanishi. All three of these last variants were still on the drawing board at the end of the war.
P1Y1-S Navy Night Fighter Byakko (White Light)
The P1Y1-S was based on standard Nakajima-produced P1Y1s. It carried two pairs of obliquely mounted 20mm cannon, one forward and one aft, but it wasn't a great success as a night fighter.
P1Y2-S Navy Night Fighter Kyokko (Aurora)
The P1Y2-S was built by Kawanishi. It was powered by two 1,850hp Mitsubishi Kasei 25a fourteen-cylinder radial engines. The nose gun was removed, but the rear-firing flexibly mounted 20mm cannon was kept, as was the internal bomb bay. In addition two obliquely mounted 20mm Type 99 Model 2 cannon were installed in the fuselage. The P1Y2-S made its maiden flight in June 1944, and a total of 96 were built. It turned out to be a disappointing fighter, with poor high altitude performance. This made it ineffective against the high flying B-29s, and so most had their obliquely mounted guns removed and reverted to being bombers, as the P1Y2 Model 16.
Engine: Two Nakajima Homare 11 radial piston engines
Power: 1,820hp at take off, 1,440hp at 18,700ft
Span: 65ft 7.5in
Length: 49ft 2.5in
Height: 14ft 1.25in
Empty weight: 15,990lb
Loaded weight: 23,149lb
Maximum take-off weight: 29,713lb
Max speed: 340mph at 19,355ft
Climb Rate: 2,133ft/ min
Service ceiling: 30,840ft
Range: 3,337 miles (maximum), 1,192 miles (normal)
Armament: One flexibly mounted 20mm cannon in nose and one flexibly mounted 20mm cannon in rear cockpit
Bomb load: 1,760lb torpedo or 2,205lb bombs