There were five models put into service, with high-explosive warheads weighing from 213.5 to 526.0 kg (471 to 1,160 lb) with effective ranges from 1,500 to 2,000 m (1,600 to 2,200 yd) at 42 kn (78 km/h).

[1] Rear Admiral Seiji Naruse led the team in charge of the initial development of the Type 91 aerial torpedo at the Yokosuka Naval Arsenal.

In their concept, a big flying boat was to carry a variant of the heavy Type 93 oxygen torpedoes to launch at long range, and then turn back towards safety.

[citation needed] The project team developed Kyoban wooden aerodynamic stabilizer plates for the Type 91's tail fins as revision 1 in 1936.

[citation needed] Before the anti-rolling controller was introduced, the early versions of the Type 91 had serious problems, as did all other aerial torpedoes of the time.

The gyrocompass and the depth meter may work well, but the torpedo cannot control the running direction by tail rudders unless they are initially in the neutral position.

[citation needed] A breakthrough on aerial torpedo design was made with the anti-rolling controller invented first by Iyeda, assistant manager of the arsenal workmen, in spring 1941.

So the Noma system was adopted for the next production version of Type 91 and it went into final testing in August 1941, making practical the use of aerial torpedoes both in rough seas and in shallow waters.

The Mitsubishi-Urakami Ordnance Works plant at Kawatana specialized in torpedo production and was destroyed by the atomic bomb dropped on Nagasaki.

[citation needed] Germany wished to acquire the knowledge behind the Imperial Japanese Navy Air Service's aerial torpedo technology in order to more effectively attack the Allied transport ships steaming in the Mediterranean Sea.

[4] It had previously imported Italian-made aerial torpedoes, which became unavailable following the Italian Armistice of Cassibile with the Allies in September 1943.

[citation needed] The Type 91 (modification 2), was a shallow-water aerial torpedo that was designed for and used in the attack on Pearl Harbor in 1941.

Wooden fins and a softwood breakaway nose cone were added to allow for launching into shallow water at low altitudes.

[7] It would have been the largest aerial torpedo in the Imperial Japanese Navy Air Force, but the operating concept became outdated and the project was never completed.

[citation needed] Some 30 years after the war, surviving members of the development team raised money to privately publish a small book, Koku Gyorai Note or Aerial Torpedo Notebook.