08/09/2025
Mitsubishi 1MT1 十年式艦上雷撃機
The Type 10 Torpedo Bomber (company code: 1MT1. The number ten refers to the 10th year of the reign of Emperor Taisho, i.e. 1921), was the third* aircraft designed by former Sopwith designer Engineer Herbert Smith ( https://en.wikipedia.org/wiki/Herbert_Smith_(aircraft_designer) ) in Japan and was Japan's first domestically produced torpedo bomber. The first prototype was completed at the Nagoya Factory on August 9, 1922. On the same day, it was test flown by pilot William Jordan and armed with a 908 lb dummy torpedo, it successfully completed its maiden flight of approximately 30 minutes at the factory airfield. Subsequently, the second prototype was completed, and further trials were conducted at Kasumigaura Airfield in November.
It was a fixed-landing-gear, single-engine, single-seat aircraft with a wooden frame covered in fabric. The first prototype was fitted with a 450-horsepower Napier Lion engine (hence the letter N in the 1MT1N designation), while the second aircraft was equipped with a 370-horsepower Lorraine engine (indicated by the L in the 1MT1L designation).
The first model was approximately 7 kg heavier due to the engine's weight, but its greater power enabled a maximum speed 13.5 knots faster under light load (1,605 kg) and a climb time to 3,048 meters reduced by 4 minutes and 12 seconds. Consequently, the type equipped with the Napier Lion engine (1MT1N) entered production, with 10 aircraft manufactured in fiscal year 1922 and 10 in fiscal year 1923, totaling 20 units.
This Type 10 Torpedo Bomber was characterized by its adoption of a triplane configuration and its single-seat design, which meant it possessed absolutely no defensive armament against enemy fighters or other threats. The triplane configuration had been employed during the First World War in aircraft such as the British Sopwith Triplane fighter and the German Fokker Dr I fighter. It offered advantages in terms of reducing airframe size, improving maneuverability, and increasing payload capacity. The 1MT was adopted precisely for these advantages. It surpassed the biplane Blackburn Swift carrier-based torpedo bomber and Sopwith Cuckoo carrier-based torpedo bomber in agility and maneuverability, while its speed and climb rate exceeded those of the Type 10 Carrier Reconnaissance Plane (Mitsubishi 2MR). However, the triplane configuration also presented the problem of increased overall height. In the case of the 1MT, when loaded onto the aircraft carrier Hosho, its height proved excessive, leaving insufficient clearance beneath the hangar ceiling and causing difficulties in handling within the ship. Being single-seat and lacking machine guns was a trait shared with the imported Swift and Cuckoo, but practical trials demonstrated the necessity for defensive armament. Consequently, development of its successor, the biplane, two-seat Model 13 Carrier-based Attack Aircraft (Mitsubishi B1M), commenced urgently and the 1MT disappeared from the list of aircraft in service in 1924.
Among the three Type 10 models designed by Engineer Smith, this was the shortest-lived. However, during its service, LTJG Kikuchi Tomozo(?), an instructor at Kasumigaura Air School, successfully ascended to an altitude of 7,620 meters in an 1MT equipped with an oxygen inhalation apparatus on July 4, 1923. This surpassed the Japanese altitude record set five days earlier by LTJG Ohashi in a Type 10 carrier fighter. Furthermore, on December 5 of the same year, this aircraft achieved the first successful aerial launch test of the 18-inch (45cm) domestically produced torpedo. This torpedo, developed at the Yokosuka Naval Arsenal based on the Type 44 45cm naval torpedo, saw its prototype completed in 1921. Following over fifty launch trials conducted by LT Akashiba and LTJG Kikuchi using the Type 10 Torpedo Bomber, it was confirmed that both the diving and running performance were significantly superior to the existing 14-inch short torpedo, leading to its adoption as the Type 44 Aerial Torpedo. It remained in service until around 1934, when it was replaced by the Type 91 Aerial Torpedo, developed from the outset as an aerial torpedo. This torpedo was transitional in nature for an air-launched type, and the 1MT itself proved short-lived. Nevertheless, its contribution in paving the way for air-launched torpedo attacks, which later achieved numerous combat successes, cannot be forgotten.
General characteristics
Single-engine triplane carrier-borne torpedo carrier. Wooden structure with fabric covering. Non-folding wings.
Crew: One pilot in open cockpit
Length: 9.779m (32ft lin)
Wingspan: 13.259m (43ft 6in)
Height: 4.457m (14ft 71/2in)
Wing area: 43sq m (462.863sq ft)
Wing loading 36.1kg/sq m (7.31b/sq ft)
Power loading 5.56kg/hp (12.21b/hp)
Empty weight: 1,370kg (3,0201b)
Gross weight: 2,500 kg (5,511 lb)
Powerplant: 1 × Napier Lion , 336 kW (450 hp)
Performance
Maximum speed: 209 km/h (130 mph, 113 kn)
Cruising speed 130 km/h (81 mph, 70 kn)
Climb to 3,050m (10,000ft) in 13min 30sec
Service ceiling: 6,000 m (19,680 ft)
Endurance 2.3 hours
Armament
1 × 457 mm (18 in), 800 kg (1,764 lb) torpedo
*The other two aircraft were the Mitsubishi 1MF carrier fighter and the Mitsubishi 2MR carrier-based reconnaissance aircraft.
