Nakajima E2N (1927)

Imperial Japanese Navy ship-based reconnaissance floatplane (1927-1936), 77 manufactured.

The Nakajima E2N (Type 15) was an IJN interwar reconnaissance, single-engine, two-seat, sesquiplane with two floats. Developed as a short range reconnaissance floatplane for catapult launch from cruisers and battleships it was ordered to replace the Hansa-Brandenburg inspired Aichi and Yokosuka monoplanes. It was selected in instead of Aichi's Type 15 in 1927. The E2N2 was a training version made in 1928-1929 and in all c80 were produced until 1929, inc. a few by Kawanishi, and 2-3 used by the civilian fishery patrol. Replaced in 1932-1933 by the E4N, they lingered in training or were sold to civil buyers. The last trainer was retired from Kasamigaura Kōkūtai in 1936

Nakajima E2N from the seaplane training squadron, Kasumigaura Kokutai, 1930s.

Development of the Nakajima E2N

The IJN (Imperial Japanese Navy) looked like a suitable ship-based reconnaissance and spotter aircraft since seeing the first British experimentations in 1918, but many believed the catapult, then still in development, was a more viable method than small wooden take-off platforms on top of turrets, notably due to the increasing weight of airplanes and due to the Pacific's wide expanses being more adapted to floatplane than land-based models, more at eas in restrctive waters for obvious reasons.

Before catapults, Japanese alrady successfully deployed Farman MF.11 1914 Ship-based light bomber floatplanes from IJN Wakamiya during the siege of Tsingtau. Many models were tested, notably both Aichi and the Yokosuka Naval Arsenal, a state manufacturer owned by the IJN, already tested models derived from the German WWI hansa-brandenburg, before deciding on biplanes instead.

Indeed right after World War I, the Imperial Japanese Navy still imported Hansa Float Reconnaissance Seaplanes as standard seaborne spotted but by 1923 (Taisho 13), the Navy ordered the Yokosuka Naval Arsenal and Aichi as well as Nakajima to develop a new float reconnaissance seaplane to replace the Hansa. Its purpose was to be a carrier-based close-range reconnaissance aircraft capable of being launched from the catapults of battleships and cruisers.

In between, the very first model seeing production was not catapulted. It was the Yokosuka E1Y, answering this 1923 request. It was designed by a former member of the Short Brothers sent in Japan and single-engined, two-bay, two-seat, powered by a 400 hp (298 kW) Lorraine-Dietrich engine. The model A which flown in 1923 showed poor performances as being overweight, and it was succeeded by the Model B which flew the next year with a lot of cweight-cutting measures, and was successful. It was accepted in January 1926 as the Type 14 Reconnaissance Seaplane (short E1Y) but was a general purpose observation floatplane, not a catapult-launched model.

As work progresses on catapults, so was the need for a dedicated model. Yokosuka Arsenal developed an all-metal Yokosuka Tatsu-go prototype, but it was rejected. Aichi developed the Type 15-A Model (Mi-go Seaplane) as well as Nakajima the Type 15-Otsu. So as the E1Y entereded service the IJN staffed foubled down on catapulted seaplane. They were scheduled to be deployed on the 1918 and 1919 light cruiser programmes as well as the 1924 IJN heavy cruisers of the Aoba class and their successors, the Furutaka.

The Type 15 Float Reconnaissance Seaplane (Ichigo Shiki Suijo Teisatsuki) thus was designed as a float reconnaissance seaplane, with tenders met by Nakajima and others, the latter co-winning wit Aichi a contract for a prototype: The Type 15 Otsu Float Reconnaissance Seaplane. At the time Nakajima was led by engineer Takao Yoshida, which developed a new single-wing design with a wide downward field of view unlike the Hansa and its poor visibility. The prototype was completed in 1924.

After review, Nakajima's aircraft was selected for adoption, as its downward field of view and flight performance were significantly superior to those of other aircraft. It was pitted also in comparative tests against the rival Type 15 Kou Float Reconnaissance Seaplane from Aichi Tokei Denki Aircraft Division. The first won its acceptance trials and was adopted in 1927. After further strengthening to withstand catapult launches and modifications to the tail, it was officially adopted in May 1927 as the first model for carrier-based catapult use, officially the "Type 15 Seaplane Reconnaissance Plane", abbeviated E2N.

About the Type 15A seaplane

With engineer Tetsuo Miki as chief designer, Aichi developed a low-wing monoplane that could be considered a modernized version of the Hansa type, completing a prototype in 1924. Although ambitious attempts were made, such as adopting a unique structure for the main wings and float struts, the prototype was unstable, and despite several modifications, including changing the center of gravity, none of the improvements were adopted, and only four prototypes were produced.

Design of the Nakajima E2N

The E2N was a classic single bay two-seat biplane with floats, built in wood and metal framing for the fuseage, wrapped in canvas, plus wood and canvas for the wings, apart for the frame core. Unlike the E1Y it was designed to be catapult-launched and thus, strongly built, plus it had folding wings. Only the nose was full-metal. Measures and specs below. It was almost 2 tons were fully loaded. The two floats were divided by bulkheads and could contain gasoline.

The E2N was powered by a Mitsubishi Type Hi V-8 water-cooled piston engine rated for 220 and tup to 250 kW (300–340 hp), mated to a 2-bladed fixed-pitch wooden propeller. It could reach 172 km/h (107 mph, 93 kn) at sea level, with an endurance of 5 hours (range unknown, circa 800 nm) but it was not lightning fast, with a climb time to 3,000 m (9,800 ft) for an anemic 31 minutes 37 seconds. It had a crew of two with a pilot and MG-gunner/observer further aft manning a flexible 7.7 mm (.303 in) machine gun.

Length:	9.565 m (31 ft 5 in)
Wingspan:	13.52 m (44 ft 4 in)
Height:	3.688 m (12 ft 1 in)
Wing area:	44 m2 (470 sq ft)
Empty weight:	1,409 kg (3,106 lb)
Gross weight:	1,950 kg (4,299 lb)
Powerplant:	Mitsubishi Type Hi V-8 water-cooled piston engine, 220–250 kW (300–340 hp)
Propeller:	2-bladed fixed-pitch wooden propeller
Maximum speed:	172 km/h (107 mph, 93 kn)
Endurance:	5 hours
Time to altitude:	3,000 m (9,800 ft) in 31 minutes 37 seconds
Wing loading:	44.3 kg/m2 (9.1 lb/sq ft)
Power/mass:	0.12 kW/kg (0.07 hp/lb)
Guns:	1 × flexible 7.7 mm (.303 in) machine gun
Crew	2: Pilot, Observer

Variants

There was the standard Type 15 Float Reconnaissance Seaplane Model 1 (E2N1) and the Type 15 Float Reconnaissance Seaplane Model 2 (E2N2), the latter having dual controls and used as seaplane intermediate trainer. Another unique variant was the Nakajima Fishing Seaplane, a three-seater aircraft for civilian fishing surveys. Two aircraft, the No. 8 Giyuu and No. 9 Giyuu, were manufactured. Even though production was limited, it was split between Nakajima and Kawanishi. Nakajima produced the E2N1 in 1927-28 plus the E2N2 in 1928-29. 47 aircraft plus two or three civilian vairants built in 1930 for fishery patrol. Kawanishi took over production for a last batch in 1929-30 of 30, for a grand total of 77+2-3.

E2N1 (Type 15-1 Reconnaissance Seaplane) Short-range standard.
E2N2 (Type 15-2 Reconnaissance Seaplane) Trainer version, dual controls.

Operational career of the Nakajima E2N

There are little records on the use of the E2N, apart its deployments on all units of the fleet as a dual role of reconnaissance and artillery spotting model: Namely on the four Kongo class battlecruisers, Fuso, Ise and Nagato class battleships (six of the latter), all the light cruisers of the Kuma, Nagara and Sendai class, the Aoba and Furutaka class heavy cruisers (4 ships) plus the four Myoko class, albeit already at this stage, replacement was on its way. Some sources says it was also deployed on the Takao class, but the latter were given E4N2 model instead.

It served as a carrier-based aircraft until early 1935, after which it was used as an intermediate trainer. Approximately 80 were produced, with Kawanishi Aircraft producing another 10 or so for civilian use, such as for mail flights. The Nakajima E2N is nevertheless significant. It was the first Japanese reconnaissance aircraft to be catapult launched and last all-wooden frontline aircraft of the Japanese Navy. Its successor was the Nakajima Type 90 (E4N).