Dubbed the Allied code-name GRACE, the B7A2 Ryusei was the largest and heaviest Japanese carrier-based attack aircraft to fly in World War II. The GRACE flew on shapely wings bent near midspan to provide clearance for a large propeller that spanned 3.5 m (11 ft). GRACE flew and handled as well as it looked, but the B7A2 never played a significant role in the Japanese war effort. Development began on this aircraft in 1941. That year Japanese Navy planners issued ambitious specifications describing a new attack bomber that, if built and selected for service, would eventually replace two different models already operational, the Nakajima B6N JILL torpedo bomber and the Yokosuka D4Y JUDY dive bomber.
The new design had to accommodate two 250 kg (551 lb) or six 60 kg (132 lb) bombs within an enclosed bomb bay, or a single 800 kg (1,764 lb) torpedo suspended beneath the fuselage. The Navy also specified these additional requirements: a heavy defensive armament consisting of two 20 mm cannons mounted in the wings and a flexible 13 mm machine gun mounted in the aft cockpit, a top speed of 570 kph (354 mph), a maximum range of 3,220 km (2,000 mi), and maneuverability that matched the Zero fighter (see NASM collection).
Navy officials understood that this large, high-performance aircraft demanded a powerful engine. They instructed Aichi to use the Nakajima Homare 11 engine, a power plant in the 1,800 to 2,200 hp-class. This radial engine was still in development but it was comparable to the very successful Pratt & Whitney R-2800. Aichi Chief Engineer, Toshio Ozaki, and his assistants, Morishige Mori and Yasushiro Ozawa, selected a mid-fuselage wing position for the new bomber. This layout, and the wing's gull-shaped kink, was necessary to provide adequate ground clearance for the under-slung torpedo. Aichi completed the first prototype in May 1942 but engine problems and other difficulties kept the firm from commencing production until April 1944. At this time, Aichi also changed to the improved Homare 12 engine.
Aichi and the Navy set up two assembly lines, one at Aichi's home factory at Funakata, and the other at the Naval Air Arsenal at Omura. Unfortunately for the Japanese Navy, the production rate never really shifted into high gear. After building the airplane for about a year, production halted at the main factory after of a major earthquake destroyed the plant in May 1945. Aichi had produced only 80 production aircraft (plus nine prototypes). The Arsenal produced another 25 aircraft, for a total delivery of only 105 bombers. To compound the problem of fielding the GRACE, the U. S. Navy had all but eliminated the Japanese carriers during the Battles of Midway, the Philippine Sea, and Leyte Gulf. With no sea base from which to operate, the handful of B7A2s delivered to navy units flew only from land bases. Most of these airplanes were destroyed in kamikaze attacks during the last months of the war.
The National Air and Space Museum's Ryusei is believed to be the only remaining example in the world. The U.S. Navy recovered from the Japanese home islands and shipped it to the United States for evaluation. Unfortunately, nothing of the bomber's operational history is known. The Smithsonian Institution accepted the airplane in 1963 and placed it in storage. It awaits restoration at the Paul Garber Facility in Suitland, Maryland. The B7A2 proved a useful resource during the restoration of another Aichi product, the M6A1 Seiran (see NASM collection). Lacking drawings and other information, the restoration staff used the GRACE on several occasions to investigate how Aichi built certain features. Some parts were also identical and, if missing or damaged on the Seiran, could be copied from the Ryusei.