Although in operational service for less than a year, the Ki-67 Type 4 heavy bomber (Allied code name 'Peggy') proved to be one of the Japanese Army Airforce's most effective and versatile aircraft. In Japanese service it was known as the Hiryu (Flying Dragon). This was the first Army bomber to carry an aerial torpedo, and was employed by the Army and Navy in the antishipping role as well as a conventional bomber, ground attack plane, reconnaissance aircraft, interceptor, BAKA carrier, and, in desperation, as a Taiatari (suicide) aircraft. Several were employed as research aircraft. A 75 mm cannon was provided in the Ki-104 variant to provide a "heavy fighter" to intercept high-flying U.S. B-29 Superfortress bombers; 40 aircraft were completed, but the concept was not successful. The Peggy was also selected as carrier for the I-Go-1A guided missile, but that weapon did not become operational before the war ended. The Peggy was flown by the Japanese Navy in small numbers as a torpedo bomber; the aircraft first saw action in this role in attacks against the U.S. Third Fleet off Formosa in Oct. 1944. Bother services continued to employ the Peggy in torpedo attacks.

Design of the Mitsubishi Ki-67 began in 1941 and the prototype flew on Dec. 27, 1942. Although flight tests were successful, modifications delayed production and by early 1944 only twenty-one aircraft had been completed. Production was happered by U.S. bombing attacks and the earthquake of Dec. 1944; a total of 698 aircraft were built.

The twin-engine, mid-wing aircraft bore a superficial resemblance to the Navy's G4M Betty bomber, with a prominent glazed nose and tail, and a large tail fin; however, the twin-engine Peggy had a dorsal hump housing the cockpit and ending in most models with a dorsal gun turret. The undercarriage retracted fully into the radial engine nacelles. An internal bay could hold up to 1,746 lbs of bombs or an aerial torpedo could be carried externally under the fuselage. Defensive armament consisted of a 20 mm cannon in the dorsal turret plus three flexible 12.7 mm machine guns and paired 12.7 mm guns mounted in the tail turret.

The Ki-67-Ib had an impressive top speed of 334 mph with a maximum range of 2,360 miles. The crew was six to eight-reduced to three for suicide attacks