Aichi S1A1 Denko - The Thunderbolt

[Would you like to see the S1A1 in-game?]
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Note: This suggestion was imported from the old War Thunder forum. While the old suggestion was passed for consideration in the old forum, I’m required to repost this again due to the “clean slate” suggestion rule.

Hello, today I would like to suggest the addition of the Aichi S1A1 Denko (電光 - Thunderbolt). This plane is a rather enigmatic heavy fighter, night fighter, and interceptor with various special quirks not found in any other Japanese WW2 planes. Due to the several problems with the engines and unfortunate circumstances, however, none of the image of the complete prototype survives today.


A model of the S1A1, showing the layouts of the plane.

In the early years of the Pacific theatre of World War 2, the Imperial Japanese Navy doesn’t find a need to create a delicated night fighter. Starting from 1943, however, the Japanese main islands found itself under threats from occasional night bombing raids by the American’s B-17 Flying Fortress and B-24 Liberator bombers, and later from the B-29 Superfortress. The high command frantically tried to convert serveral existing aircraft to counter American bombers, such as the IJA’s Ki-109 and IJN’s P1Y2-S Kyokko, both of which, as well as other conversions, were unsuccessful due to it being unable to climb and reach the targets.

On 21 May 1943, a field-modified Nakajima J1N1 recon aircraft fitted with two 20 mm Type 99 cannons at an upwards angle managed to shoot down two B-17 bombers at Rabaul. This modified version of the J1N1 was a brainchild of Commander Kozono Yasuna of 251st Kokutai, who ordered the modification against high command’s orders who were skeptical about his idea. After this success, the high command’s preception of a delicated night figher interceptor has changed. The IJN would have later placed order for Nakajima to produce an interceptor variant of the J1N1 and saw great success against B-17 and B-24, whose utilizing a quirky ball turrets and cannot keep up with the plane.

However, when the B-29 made its debut in late 1943, the J1N1 is now somewhat inadaquate against the new threats. As the B-29 is able to fly at an altitude that the J1N1 barely reach, is fast enough that only one pass can be done to attack them, and is equipped with a remote-controlled turrets that can dispatch the J1N1 down. The IJN again found itself under the threat that they were unable to effectively counter.


Original design blueprints of the S1A1, note the slightly different nose shape.

Thus, in the end of 1943, the IJN issued the 18-Shi Hei order for a new delicated heavy night fighter and interceptor capable of reaching the altitude of the B-29. The specification required the plane to reach a maximum speed of 685 km/h at an altitude of 9,000 m, able to climb up to 6,000 m altitude in 8 minutes, 5 hours of flight duration per sortle, armament consisting of at least two 30 mm cannons, and mounted with radar equipment. Aichi aircraft company later accepted the order in November 1943, as they doesn’t have any urgent orders like the other company at that time.


A blueprint of the S1A1, a hardpoint for 60 kg bombs and extra fuel tanks can be seen at the top.


Internal design of the S1A1, an airbrake and elevation mechanism for the frontal 20 mm cannons can be seen in the image.


The S1A1’s wing structure.


The S1A1’s control panel.


Blueprint of the nose section of the S1A1. There is the list of the components; 1) Antenna for TAMA 3 centrimetric radar 2) 30 mm 17-shi (Type 5) cannons 3) 20 mm Type 99 model 2 cannons in default frontal firing position 4) Elevation mechanism for Type 99 cannons to be fired in Schrage musik configurations 5) Aiming sight 6) Two 60 kg bomb hardpoints below the nose 7) 250 kg bomb hardpoint slightly behind the 60 kg bomb hardpoints.

The plane was given a unique designation of S1A1 by the IJN, as it was the first delicated night fighter project. The plane will be an all-metal, tail-dragging design with only its control surface is covered with canvas. The aircraft will be fitted with several advanced features not found in most of Japanes airplanes, such as hovering flaps and air brakes on the bottom of the fuselage and wings, oxygen-injected turbochaged engines, pressurized cockpit, a basic TAMA 3 search radar, and a remote-controlled turret with wide coverage.

The crew consists of two men; a pilot, and a gunner who sits behind the pilot in a small dome cockpit. The gunner utilize the remote-controlled rear turret which can be fully rotated and can aim upwards to hit enemy aircraft from below.

The main armaments consists of two 30 mm Type 5 cannons and two 20 mm Type 99 model 2 cannons (although some sources say that it was the earlier model 1 cannons), the nose-mounted 20 mm cannons have a special mechanism to elevate the gun at 30 degrees of angle to turned it into a “Schrage musik” guns to hit the bomber’s belly. The remote-controlled turret is fitted with two 20 mm Type 99 model 2 cannons and is able to fully elevate up to 90 degrees, again to deal the hit from below. The aircraft can be loaded with one 250 kg bomb under the fuselage hardpoint, or two 60 kg bombs hooked on a small hardpoint benearth the nose.


The S1A1’s engine configurations and landing gear mechanism.

Aichi finished the S1A1’s design in May 1944 and completed the mock-up in August 1944. When Aichi has started building the two prototype ordered by the IJN, however, they found that the estimated final aircraft is somewhat overweighted at 10 tons full load, and that the Navy-issued Nakajima Homare 22 engines is not powerful enough to power the S1A1 to its specified top speed. Aichi then scrambled to find a way to increase the engine power, such as trying to develop a new turbochargers, then changed to an oxygen-injected engine, and finally planned to change the engine into Nakajima Homare 24. Which caused the construction of the two prototypes to be delayed by several months.


1856161338_AichiS1A1.jpg.7370539f3c06cb9 s1a-2.jpg.758ec11a43b7b791e62a90d734d9d1

The S1A1’s mockup under construction. Unfortunately, none of the image of the actual prototype survives today.

On 7 December 1944 (3 years after Pearl Harbour attack), the Tonankai earthquake, an 8.1 magnitude earthquake occured. The earthquake heavily damaged the Tokai region where the S1A1’s prototype is being constructed and the prototype is badly damaged. The two prototypes would meet its untimely end in 1945, with the first prototype (70% completed) were destroyed in a bombing run in 9 June 1945, and the second prototype (90 - 95% completed) which were relocated to Gifu were destroyed in another bombing run in 9 July 1945.

While the S1A1 is never completed, with the second prototype being very close to completion. In War Thunder, the Denko will fulfil a similar roles with the American counterpart; the P-61 Black Widow. The S1A1 is well equipped and well-protected enough to take down any aircraft at its rank, and will provide a unique experience for the Japanese pilot.


General characteristics:

Crew: two, pilot and gunner

Length: 49 ft 6.5 in (15.1 m)

Wingspan: 57 ft 5 in (17.5 m)

Height: 15 ft 1.5 in (4.61 m)

Wing area: 505.902 sq ft (47.0 m2)

Empty weight: 16,138 lb (7,320 kg)

Gross weight: 22,443 lb (10,180 kg)

Max takeoff weight: 25,375 lb (11,510 kg)

Powerplant: 2 × Nakajima NK9K-S (Homare 22) , 2,000 hp (1,500 kW) each at take-off

Propellers: 4-bladed


Maximum speed: 360 mph (580 km/h, 318 kn) (estimated)

Cruise speed: 273 mph (440 km/h, 240 kn) (estimated)

Range: 1,054 mi (1,697 km, 916 nmi)

Ferry range: 1,553 mi (2,500 km, 1,373 nmi)

Service ceiling: 39,370 ft (12,000 m)

Wing loading: 44.4 lb/sq ft (126.6 kg/m2)

Climb to/in: 29,530 ft (9,000 m) in 14 min 45 sec


Offensive: 2 × 30 mm Type 5 cannons and 2 × 20 mm Type 99 model 2 cannons in adjustable mounts

Defensive: 2 × dorsal turret-mounted 20 mm Type 99 model 2 cannons in a flexible remote-controlled turret

Suspended: 1 × 250 kg bomb or 2 × 60 kg bombs

Radar: TAMA 3 search radar



Francillon, Ph.D., René J. Japanese Aircraft of the Pacific War. London: Putnam & Company Ltd.,

Japan Project Aircraft: Koei, ISBN 4-87719-490-8 C0031,
Imperial Japanaese Navy Warplanes: Green Arrow, ISBN 4-7663-3161-3 C0076

Aichi S1A - Wikipedia電光 (in Japanese)

Уголок неба ¦ Aichi S1A Denko (in Russian)ô-night-fighter-am-25.6535/

Aichi S1A Denko Info

Aichi D1A Denko (Bolt of Light)


Glad to see this suggestion again +1


Yes please! +1

This would be a unique addition to the Japanese tree. It would be the only WWII-era Japanese plane in-game to be equipped with air-search radar, and the dual 20 mm turret would be excellent as both an offensive weapon (against bombers primarily) and defensive gunner (much better than the gunners on in-game Japanese heavy fighters). This is not to mention that the Japanese heavy fighter standard armament of 2x20 mm and 2x30 mm cannon would be capable as usual. The functionality of elevating the nose-mounted 20 mm cannons would also be an interesting new feature.


This is really cool! Would love to have it. +1

Definitly and gladly I have some ORIGINAL FIRST HAND MATERIALS received from aichi kokuki kk’s decsendents, I’d like to provide such precious materials and blueprints to those who also love this plane and to Gaijin. I’ve studied this plane for a long time.


That’s very cool and interesting to hear i wouldn’t mind learning more.

Yes yes yes please +1 such a beautiful aircraft

1 Like

Would be awesome if you could share them

1 Like

I will give some instructions here, if anyone extremely want these first hand resources, please email me [email protected].

So first, this thing was called AM25 or A90 by Aichi and S1A1 by the navy, she also had a name “18-shi Hei Sen(Type C fighter planned at Showa 18)”. Denko was designed by Ozaki who also designed B7A and D4Y in the game. Denko has many characteristics that made her quite different from other Japanese fighters. The following information comes from “Denko Plan Instruction Report”, created at 1944.2.13.

  1. This plane’s fuselage was very light compared to her heavy overall-weight, with only 360kg for her fusalage weight. This is because Aichi used the same technology that induced the success of Saiun.
    Before saying that, I would like to intoduce the structure of an fuselage. A fuselage normally should consist the following parts: frames (ring like structure that hold the entire fuselage), stringer that connect the frames, longeron which is a type of thickened stringer that not only connect the frames but also strengthen the entire aircraft, and finally the skin.
    For most of the planes that would work, but for Denko, she abandoned one of the above, the stringers.
    The IJN had found that, the weight of a plane would be reduced if you deleted all the stringers and let a few but strong longeron take over the work of frame connections, also the skins are thickened so they could also take some pressure during manovering.
    Denko also has such design. Her fuselage also had five parts in order to reduce production time: the front part, with one 30mm gun and two 20mm guns, the cockpit part, the fuselage-main wing part which connect the main wing, the middle part which has a 20mm turret, and the back part.
    Her fuselage cut-view was also weird, when you take a look at the slice of her fuselage, you will see that even if the slice view of the front part, the cockpit part, and the main wing part was circle and oval like other planes, but from the beginning of the middle part, the slice view became a square. This made the 360 degrees 20mm turret able to turn and do its job.
    About the materials, the frames are made of SDCH and SDCR, the longerons are made of ESD (very strong mateiral), the skin were partly made of SDCH and SDCR, and a few parts are made by wood (the nose, the upper door for front gun maintainance, the belly of cockpit part, the skin around the cockpit’s window, the upper and bottom skins of middle part, the vertical stablizer, and the door for the landing gear’s doors).
    Specifications about her fuselage:
    Length: 14.65 meters
    Width: 1.25 meters max
    Height: 1.348 meters (without cockpit window)
    1.726 meters (with cockpit window)
    Height from the floor of cockpit to the top of cockpit window: 1.052 meters
    Height from the floor of recon seat to the top of recon window: 0.922 meters.
  1. About Denko’s wing
    in order to obtain the max speed given by the navy, Denko has many new designs on her wing.
    First, she obtained the He100-style wing structure, this is a kind of laminar flow wing which reduces the resistance and gives her high speed. Second, her dihedral is also unique, in order to maximize the range of view from the cockpit during landing and taking off at night, the main wing was separated into to two different parts: the inner part from the connection part of fuselage to naccelle with a dihedral of 2 degrees 30’, and the outer part from the naccelle to the tip with a dihedral of 6 degrees. This design allows the maximization of Denko’s cockpit view and at the same time maximize the dihedral to give her enough balance during night operations.
    Since Denko’s wing structure is the He100 style, the drawback of laminar flow wing has also be introduced: the high wing load and bad landing stabiity due to low lift. Ozaki gives Denko a set of flaps with two slices (same design on B7A in the game) to maximize her lift, also the inner ailerons also have the same structure, they behave like normal ailerons during flights but behave like flaps during taking off or landing (the outer ailerons are just normal ailerons with one piece). Also the wing tips are also connected to the flaps, when the flaps are into position, the main wing tips would also raise up 30 degrees to maximize the dihedral.
    The horizontal stablizers are also connected to the flaps, they would change their angle of incidence from 1 degree 30’ to 3 degrees when the flaps are into position.
    Finally about the materials: the ribs are SDCH, the two spars are ESD, and the skins are SDCH and SDCR. The main wing’s tips are made of wood, the inner slice of flaps are also wood, the outer slice of flaps and ailerons are tinning, the naccelles are also SDCH and tinning. The horizontal stablizers are SDCH ribs, SDCH skins, and two ESD spars, the elevators are tinning, the horizontal stablizer is wooden and the radder is made of copper.
    Specifications of her wings:
    Main Wing:
    Width: 17.5 meters
    area: 47 square meters
    chord length(wing-fuselage connection part) :3.9 meters
    ‘’ (tip): 1.53 meters
    " (mean):2.895 meters
    Aspect ratio: 6.5
    Taper ratiao:1/2.55
    Angle of incidence (wing-fuslage connection) :2.5 degrees
    " (tip): 1.5 degress
    Dihedral(inner wing):2.5 degrees
    " (outer wing): 6.5 degrees
    " (mean): 5 degrees
    Former-back angle (angle of the front of the wing): 5 degrees 25’
    Latter-push angle (angle of the back of the wing): 9 degrees 59’
    Type of wing: He100
    Camber: 1.5%
    Position of greatest sthickness: 36.6%
    Position of greatest camber: 36.8%
    R/t: 1.2%

Horizontal stablizers:
width: 6.7 meters
chord(fuselage part): 2.1 meters
" (tip): 0.9 meters
area: 9.86 square meters
angle of incident: 1 degree 30’
volume: 0.6

width: same as horizontal stablizer
chord: 28% of the chord of horizontal stablizer

Veritical stablizer:
height(from the middle of horizontao stablizer to tip): 2.15 meters
chord(fuselage part): 2.38 meters
area: 3.42 square meters

height: 2.525 meters
chord: 0.65 meters
area: 1.24 meters


Sooo any news? Lol