Yokosuka E14Y "Glen" (1941)

Submarine-launched seaplane, 123 built 1939-43.

Development

Origins

The Yokosuka Type 0 Small Reconnaissance Seaplane (in Ordnance E14Y, Allied Intel "Glen") was a floatplane initially planned and designed to operate off a submarine. This was closely intertwined with the very concept of aicraft operated from submarines, a combination born in 1918 at least in concept and realized first by the Royal navy on its massive M2. It was clear that the solution by then was to adopt a cyclindrical hangar and having a fully folding aircraft. However catapult were just on paper and operation was by using crane, and the floatplane took off and landed at sea. Operations, from surfacing to launching the seaplane were agonisingly long.

In the early 1920s (before the signining of the Washington Treaty) the concept of cruiser submarine was strongly considered by all belligerents, just digesting late German operations with their "U-Kreuzer". The USN even had fantastical concepts of true "submarine aircraft carriers" like the BuC&R 1920 10,000 tonnes Type 1 whoch had three triple turrets and four seaplanes... Of course the treaty immediately cut short these new adventures. Caught by the signing, the British X1 and French Surcouf, already built and close to launch, were excepted. Surcouf was a cruiser submarine operating a small Besson seaplane, stored in a rear CT hangar, mounted and put at sea by a crane, retreive the same way.

But this was long to operate. Plus the small Besson was hardly capable of long range. What this gave to the French as a capacity was indeed a potent commerce raider that could have its own reconnaissance asset was capable of a 200 km range (125 miles) around the submarine, well beyond the horizon, reporting ships in real time thanks to a small radio set. The submarine was designed with a heavy turret to deal with large ships when surfaced, had a generous torpedo capacity, and even additional rooms to take onboard crews from sunken ships in a typical "prize rule" observed by France and others.

The Japanese Imperial Navy, always searched for a competitive advantage top offset its frustrating numerical inferiority as desifned as Washington, especially compared to the US Navy, prime suspect for a future confrontation in the pacific, so in its planned sphere of influence. Among the concept developed were "cheating" cruisersn destroyers and torpedo boats, using tricks to lower tonnage and maximize firepower, aicraft carriers just below the 10,000 tonnes limit passing for auxiliaries and thus unlimited, or seaplane tenders designed to be convertible as full carriers in wartime, or the Type 93 "long lance" torpedo, the development of offensive land-based naval aviation such as the Mitsubishi G3M, or the very long range, very agile A6M fighter.

The aircraft carrying IJN submarines

But the concept of cruiser submarine with seaplane was never lost on the IJN staff, but there was no coherent doctrine for the development of such submarines, certainly not on the traditional commerce raiding sense. It came at last under the leadership, here again, of admiral Yamamoto Isoroku. He saw the use of aircraft-launching submarines for extended reconnaissance, first and foremost. The J class and later the B class submarines were created for that purpose from 1934 onwards. They had a forward catapult, immediately forward of the tube-like hangar located, buried in the outer hull, at the foot of the conning tower. This enabled to quickly extract the seaplane, mount it on the catapult, to be ready for a launch. The goal here was to located the enemy fleet and used the submarines to sink part of it and "restore the balance" for a decisive battle with the IJN main battle fleet.

The J1M was a single experimental boat (I5) followed by J2 (I6), J3 (I7,8), A1 and A2 classes (I-9 to I12) and maturation came with the numerous B class planned for long range (16,000 nm) reconnaissance in the 1937 and 1939 programmes, launched in 1939-41 (B1), 1942-43 (B2) and 1943-44 (B3) for 24 boats total from I15 to I39, displacing 3,650 tonnes submerged, with six bow TTs, a single 140 mm/40 gun (5.5 in), two 25 mm AA and a single aircraft. Later were designed for coordination between these flotillas the very lage AM command class submarines (1944) having two reconnaissance seaplanes onboard and of course the famous STO class which had a far larger hangar for three attack seaplanes, the Kawanishi E15K notably to attack the Panama canal gates.

The Watanabe E9W1 was indeed the very first Japanese submarine-carried aircraft, requested all the way back to January 1934 for the then J-3 type submarines. The first of three prototypes flew in February 1935. It could be reassembled in 2 minutes 30 seconds, disassembled in 1 minute 30 seconds. It was successfully tested on I-5 for a production batch of 32 E9W1, but only six E9W1s "Slim" operational in December 1941 albveit entering service in 193 as the Navy Type 96 Small Reconnaissance Seaplane and quicly replaced by the Yokosuka E14Y monoplane. It remained front-line until July 1942, directed their moth submarines onto Chinese ships attempting to pass the Japanese blockade in the the South China Sea.

But the type of seaplane planned for the B class were clearly smaller, with stringent specifications to be foldable and fit inside a much restricted space. This task was given to the Yokosuka Naval Air Technical Arsenal. Unlike other private companies like Mitsubishi and Nakajima, Yokosuka (also called Kugisho) was a state-sponsored company, equivalent of the US Aeronautical Division of the Navy’s Bureau of Construction and Repair, NC. Yokosuka was entrusted with a very small, very compact design, yet capable enough in speed and range, while not requiring a heavy payload.

Long story short, the model tested in 1939 perfectly suited the needs of the IJN and was tested in conditions. When approved as the Type 0 Small Reconnaissance Seaplane" (零式小型水上偵察機), it was ordered to equip all these 26 submarines plus spares for losses and training. Production went on slowly given the high specialization of this model from 1941 when introduced to 1945, for 126 delivered total. By the time the last arrived, the B class submarines still around had been converted to Kaiten motherships. They took other roles.

Detailed development

The creation of the E14Y1 floatplane followed the third program (Otsu 3) to improve the IJN, implemented in 1937. Yhe navy developed the 12-Shi specificatio for a replacement of the Watanabe E9W1. It was created on a competitive basis, but the staff took all measures to ensure maximum secrecy. Kugisho and Watanabe Tekkosho took part in this competition and already at the initial stage the Kugisho project was more promising (hence the name stuck, despite production was done by Yokosuka). The Kugisho engineering team headed by Mitsuo Yamada and his time found the project quite challenging, to achieve a model with excellent flight characteristics, while not exceeding stringent overall dimensions. Yamada preferred a monoplane, low wing configuration with two supporting floats. In the hangar, the wing consoles could fold along the fuselage, stabilizer turned downwards (hence its off shape).

At the end of 1938, the first two prototypes were completed, earning the designation "2-Shi marine experimental boat floatplane E14Y1". In early 1939, flight tests started in Tokyo harbor under supervision of pilot Lieutenant Okane and observer Kato. Like its predecessors it was very compact and twin-float, and the 9-cylinder Hitachi GK2 Tempu 12 was chosen as being also a very compact air-cooled unit, and also to gain space, coupled with a wooden two-bladed constant-pitch propeller.

During weight control, the model turned out at 1,130 kg, exceeding calculations by 180 kg quite an enormous margin. As a result, the payload was reduced and the Navy not pleased with Kugisho's engineers. The fuel tanks was also reduced to 200 liters making the useful range lower by 480 kilometers. It just not perform its primary reconnaissance missions, and that impacted the new class of submarines about to enter service. The third and fourth prototypes were then give, along with the plans, to Watanabe lightened by 80 kg. The initial insufficient directional stability was also corrected by installing a small additional strut under the fuselage and increases the area of the main keel. In December 1940 it was accepted into service as E14Y1 I-1, later simplified as E14Y1 11. Internded for submarines, it was also patrol the home island coastal waters from seaplane bases, especially after 1943. Production was given K. K. Watanabe Tekkosho between 1941 and 1943.

Design

Kugisho, then Watanabe, created a true "origami" of a plane, with arrangements of folding tubes enabling to literrally "popup" the plane in no time once extracted from its storage tubular "hangar". The fuselage structure consisted of metal tubes. The skin in the nose was made of sheet duralumin, and the central and tail sections of the fuselage were covered with fabric. The wing was of mixed construction with metal spars and wooden ribs. The wing skin was completely made of fabric. The tail unit had a similar design. The floats were all-metal. The crew cabin was closed with a transparent canopy and had sliding sections that provided access to the crew. The aircraft's defensive armament consisted of one 7.7 mm machine gun mounted on a pivot mount in the observer's cabin. The aircraft could carry two 30 kg bombs on wing bomb racks.

The E14Y1 was placed fully folded in a watertight oval-shaped hangar 1.4 m high, 2.4 m wide and 8.5 m long located on the deck, in front of the conning tower and partly buried in the outer hull, above the pressure hull. It was broken down into 12 components. The floats were detached from the wing and fuselage as the straight wings, laid along the fuselage, fixed in this position with clamps. The tail unit was folded, stabilizer and elevator turned up, and the keel was turned down. From surfacing until launch from the 20 meter inclined steel tracked pneumatic catapult on the forward deck, 15 minutes passed. It was way more than initially planned, and more than the model its replaced. With modifications and training, it was lowered to 6 minutes 23 seconds. After flight, the E14Y1 landed near the submarine to be lifted on board by a crane, disassembled and placed in the hangar.

specs.
Length:	8.54 m (28 ft)
Wingspan:	11 m (36 ft 1 in)
Height:	3.8 m (12 ft 6 in)
Wing area:	19 m2 (200 sq ft)
Empty weight:	1,119 kg (2,467 lb)
Gross weight:	1,450 kg (3,197 lb)
Max takeoff weight:	1,600 kg (3,527 lb)
Crew:	2: Pilot/Observer/gunner
Propulsion:	Hitachi GK2 Tempu 12 9-cyl. ACRPE 250 kW (340 hp) TO 220 kW (300 hp) SL
Propeller:	2-bladed wooden propeller
Maximum speed:	246 km/h (153 mph, 133 kn) SL
Cruise speed:	167 km/h (104 mph, 90 kn) at 1,000 m (3,300 ft)
Service ceiling:	5,240 m (17,200 ft)
Time to altitude:	3,000 m (9,800 ft) in 10 minutes 11 seconds
Range:	881 km (547 mi, 476 nmi)
Wing loading:	76.3 kg/m2 (15.6 lb/sq ft)
Power/mass:	0.1749 kW/kg (0.1064 hp/lb)
Armament:	1× rear 7.7 mm Type 92, 2× 76 kg (168 lb) bombs
Total production	123

Combat

The first operational use was to survey the effects of the Pearl Harbor attack, ten days later. Another "Glen" was launched off the West Coast of the USA and famously dropped bombs in the forest of Oregon from I-25. This wa sprobably the best known high profile mission and actually the only Japanese attack of American soil. They were also used for reconnaissance over Australia, New Zealand, the Aleutians. But it was disliked by pilots, being slow and not particularly agile, it was easy target for Allied aircraft. They could fly of 5 hours and often under the cover of darkness, either dusk or dawn to avoid detection.

In January-February 1942, several "Glen" made flights over Pearl Harbor. At that time, they were operated by I-7 to I-11, and I-15 to I-35. On 26 February 1942, I-25 (Captain Akiji Tagami) launched its E14Y off the northern tip of King Island, Bass Strait, off the coast of Victoria, Australia. It made the very first wartime reconnaissance over the Port of Melbourne, without opposition as this was completely unexpected. The pilot and observer were in the air for three hours, successfully mapping Port Phillip Bay, observing ships at anchor off Melbourne.

The E14Y is the only Japanese aircraft to ever overflew New Zealand during the war, after the German Friedrichshafen FF.33 'Wölfchen' in the previous war: On 8 March 1942, Nobuo Fujita photographed the Allied build-up in Wellington harbour, coming from I-25. On 13 March, he flew over Auckland, and I-25 proceeded to Australia. On the night of 24/25 May, Susumo Ito flew a "Glen" over Auckland from I-21. Later it proceeded ti the sole Japanese attack on Sydney Harbour with bombs. They claimed 21 seamen of HMAS Kuttabul, crippled, sunk on 1 June 1942.

The E14Y also famously dropped bombs on the United States. This was known as 'The Lookout Air Raid'. On 9 September 1942, Chief Warrant Officer Nobuo Fujita and crewman, Petty Officer Shoji Okuda, were launched from I-25 off the coast of Oregon; near Brookings. It carried 76 kg (168 lb) incendiary bombs intended to cause forest fires. And this succeeded moderately due to athmospheric condition and moisture that day, burning just 16 km (9.9 mi) due east of Brookings. The aircraft was spotted by Howard "Razz" Gardner from his fire lookout tower on Mount Emily, Siskiyou National Forest. He also saw the smoke plume and vectored firemen. Its seems the pilots, impressed by the size of the trees, feared being too low and dropped from the bombs from an incorrect height. In any cases, the firemen contained the fires that night, and the soil was already wet after a previous rain storm.

The FBI made an enquiry later, retrieved bomb fragments and reconstituted the bombing. Before that, Fujita attempted a second attack on September 29, but this was not more successful. This story was covered later by the press and made a sensation. Amazingly, 20 years later, Fujita was invited back to Brookings. Despite his apprehensions, he was welcomed and even became honorary citizen, donating his sabre to the town. In 1998 part of his ashes were buried by his dauthter on the bomb crater site, where he already planted a "peace tree" previously.

Surviving aircraft:
Aviation History magazine reported in the November 2008 issue that divers found and airplane in the Akibasan Maru wreck in Kwajalein Atoll waters, sunk on 20 January 1944, rediscovered in 1965. This was identified in April 2008 as from two E14Y1 floatplanes. Unfortunately none of these models survived to this day. With such small production and limited, "niche" use, the Kugisho E14Y remains a footnote in the history of the IJN.

Gallery

E14Y1 of the 2nd Sensui Sendai on submarine I7

E14EY1, 6th Kantao Fukuyama NAS December 1944

Refs

Francillon, René J. (1979). Japanese Aircraft of the Pacific War. London: Putnam & Company.
Green, William. War Planes of the Second World War, Volume Six: Floatplanes. Macdonald & Co 1962.
Ishiguro, Ryusuke and Tadeusz Januszewski. Kugisho E14Y "Glen". Sandomierz, Poland/Redbourn, UK: MMP Books, 2010.
Jackson, Robert. The Encyclopedia of Military Aircraft. Bath, UK: Parragon Books, 2006.
Januszewski, Tadeusz. Japanese Submarine Aircraft. Sandomierz, Poland/Redbourn, UK: Mushroom Model Publications, 2002.
Passingham, Malcolm (February 2000). "Les hydravions embarqués sur sous-marins".
The IJA and the IJN reconnaissance aircraft, cargo carrier, trainer and flying boat. Famous aircraft of the world special edition, Bunrindo, Tokyo 2010
Passingham, Malcolm (March 2000). "Les hydravions embarqués sur sous-marins". Toute l'aéronautique et son histoire
Thorpe, Donald W. Japanese Naval Air Force Camouflage and Markings World War II. Aero Publishers, 1977.
airwar.ru
militaryfactory.com
pwencycl.kgbudge.com
combinedfleet.com
wetwing.com
sas1946.com
pacificwrecks.com
j-aircraft.com/
en.wikipedia.org
secretprojects.co.uk