The 15-Shi requirement that produced the Ginga asked for a genuinely multi-role machine — a fast twin able to level-bomb from altitude, dive-bomb accurately, and carry a torpedo for anti-ship strikes, all in one airframe. Chief designers Tadanao Mitsuzi and Masao Yamana chased that goal with an aerodynamically clean design that drew inevitable comparisons to fast Western twins like the de Havilland Mosquito and the B-25.

The trouble with a jack-of-all-trades is that it stretches the design thin. The Ginga could perform each of its missions adequately, but the sophistication needed to do so — and above all the high-strung Homare engines chosen to give it speed — made it complex and maintenance-hungry at exactly the moment Japan was running short of fuel, spare parts and trained mechanics. It is a textbook case of an advanced design outrunning the industry meant to support it.

The Nakajima Homare (NK9) was an 18-cylinder, twin-row air-cooled radial that promised big power in a compact package — roughly 1,820 hp at take-off on the P1Y1. In theory it was exactly what a fast bomber needed. In practice it was one of the most troublesome Japanese engines of the war, sensitive to fuel quality and maintenance standards that a collapsing 1944–45 supply system could rarely meet.

The result was chronically low serviceability: many Ginga sat on the ground waiting for parts or attention while relatively few were flyable at any moment. The later Kawanishi-built P1Y2 series switched to the more dependable Mitsubishi Kasei radial specifically to escape the Homare’s supply and reliability problems — an implicit admission of how much the engine had hobbled an otherwise excellent aircraft.

As American night raids intensified, the Navy converted Ginga airframes into radar-carrying night fighters, generally listed as the P1Y1-S Byakko (“White Light”) and the Kawanishi P1Y2-S Kyokko (“Aurora”). Sources genuinely disagree on which designation applied to which conversion, so the naming should be read with caution. Both mounted 20 mm cannon angled to fire obliquely upward — the same tactical idea as the German “Schräge Musik” installations, letting a fighter attack a bomber’s vulnerable underside from below.

The concept was sound but the airframe was wrong for the job: laden with radar and cannon, the Ginga lacked the high-altitude climb and performance to reliably reach and hold a firing position under a B-29. The night-fighter experiment was largely a failure, and many of the converted machines were sent back to bombing units or, in the end, to special-attack (kamikaze) duty.

There is no credible unit cost or cost-per-flight-hour figure for the P1Y Ginga in the public record. It was a wartime product of the Imperial Japanese Navy, procured through the Navy’s own arsenal-and-contractor system rather than sold on any open market; contemporary yen pricing was not published, and much wartime industrial documentation was destroyed in 1945.

Any specific dollar or yen figure attached to a Ginga online should be treated as unverified. What is well established is the scale of the effort: roughly 1,100 aircraft were built, the great majority by Nakajima, with a smaller batch of the Kasei-engined P1Y2 series by Kawanishi — a substantial investment for an aircraft that spent much of its short life grounded for maintenance.