special attacker Aichi M6A1 Seiran: Submarine-launched Attacker

[aizenns 3,591]

Aichi Aircraft

M6A1 Seiran / 試製晴嵐

Aichi M6A1, at Smithsonian National Air and Space Museum

 

 

History

M6A1 "Seiran" was Japanese naval special attacker developed by Aichi aircraft during WW2.

In the end of 1941, IJN start project of "Special-Type Submarine". Former submarine-launched aircraft is only for recon plane but this large submarine planned to equip attacker. For this project Navy order to Aichi new float-plane attacker in 1942.

Planned plane was twin float seaplane that based No.13 Experimental Carrier-based Bomber (Kugisho D4Y). Fixed machine gun was removed for weight and rear swing machine gun replaced to 13 mm single machine gun.

 

At first this plane planned for commerce raiding in enemy rear sea area. In the early plan Special Type submarines will used for attack American sea lane of Atlantic coast. Because of it this plane designed for recon to search enemy cargo ships or bomb them with 250 kg bomb. But after Battle of Midway, IJN Grand Fleet (Perhaps Admiral Yamamoto) require to build submarine that equip torpedo. To equip 800 kg bombs or torpedo, need to remove floats. Also need to train pilots they build ground version, M6A1-K. ("-K" means this plane redesigned for trainer). Now sometimes M6A1-K called "Nanzan"(南山), but actually that trainer called "Seiran-Kai". "Nanzan" was one of the name of design that did not have floats and launched from catapult.

When equip 800 kg bomb or torpedo, pilot leave plane on the carrier sub to descend by parachute.

 

Production of M6A1 started in 1944, but production rate of this plane is only 2 per month. First reason was that number of I-400 class and I-13 class was only 5 so no need to produce a lot. Second reason was huge earthquake, "1944 Tonankai Earthquake"(Mj: 7.9) and "1945 Mikawa earthquake"(Mj: 6.8) and bombing of B-29 destroy factories and infrastructures of Aichi pref.

 

First prototype was completed in November 1943. Production number of M6A1 and M6A1-K was only 28. (Prototype: 8, Production: 20)

 

This plane is known the operation to attack Panama. Research of this operation was completed in May 1945 and submitted to GF but this project was denied because this operation fill be feasible after October and if attack Panama reinforcement of Pacific fleet will delay but in that time they already lost sea superior around Japan so there aren't any value. Also if there are enough fuel. do this operation fuels and other submarines run out.

In that time they need recon and attack to allied fleet on Ulithi Atoll for Battle of Japan. I-400 class and Seiran was valuable force that able to attack them so I-400 and I-401 equip Seiran and dispatch to Ulithi but before engagement Japan was surrender so this plane did not fought.

 

Now one M6A1 exist on Smithsonian Museum. (Serial number 28)

https://airandspace.si.edu/collection-objects/aichi-m6a1-seiran-clear-sky-storm

 

Pros & Cons

Pros

• Good speed: 470 km/h
• Good bomb loads: 800 kg bomb or Type 91 torpedo
• Float plane is easy to cap zone in Naval battles
• Able to purge floats

Cons

• Did not have fixed machine guns

 

 

Specification

Quote

 

Spoiler

Structure

• Single engine, single lower wing, twin float
• Wing: All metal, monocoque
• Flap: Double Slotted
• Body: All metal, monocoque
• Landing gear: All metal, single pillar float (Able to dumping)

Specification

• Crew: 2
• Engine: Aichi Atsuta Model 32, water-cooled V12 engine (AE1P)
  • 1,400 HP at take off
  • 1,340 HP at 1,700 m
  • 1,290 HP at 5,000 m
• Wing area: 27 m2
• Span: 12.26 m
• Length: 10.64 m
• Height: 4.58 m
• Overload weight: 4,729 kg
• Max speed: 254 knots (470 km/h) at 4,000 m
• Cruise range: 610 miles
• Climbing time: 8 min 9 sec to 5,000 m
• Sealing altitude: 9,600 m
• Armament
  • Rear gunner: 1x 13.2 mm Type 3
  • Bomb/ torpedo loads
    • 1x 250 kg
    • 1x 800 kg (when purge float) 
    • 1x Torpedo (when purge float)

 

Photos

Spoiler

Quote

Seiran with 250 kg bombs

 

 

Sources

Quote

Nozawa Tadashi (1981) "Encyclopedia of Japanese Aircraft, Vol. 2 (Aichi and Kugisho)", Shuppan-Kyodosha, page 108-114

ISBN: ?

NDL online

Quote

Kawasaki Manabu (2011) "Carrier-Based Airplanes and Seaplanes of the Imperial Japanese Navy" Dainippon-Kaiga, page 168-171
ISBN: 978-4-499-23037-7

NDL Online

Quote

http://www.nids.mod.go.jp/military_history_search/SoshoView?kanno=098

JDA Defense Training Center War History Room (1979) "Sensi Sosho Vol.98, History of Submarine", Asagumo Newspapers

page 173-174 (PDF page 101-102)

Quote

http://www.nids.mod.go.jp/military_history_search/SoshoView?kanno=095

JDA Defense Training Center War History Room (1976) "Sensi Sosho Vol.95, General History of Naval Aviation", Asagumo Newspapers

Attached Sheet No.1 "Table of specifications of Naval aircraft" (PDF page 258)

 

[leroyonly 4,311]

Open for discussion. 

[Milocat 4,857]

Oh, yes.  I've wanted this plane for a long time.  Such a beautiful aircraft.  +1.

[Z3r0_ 4,128]

It's been suggested before, and I still support it, even its maximum payload would be a bit anemic at 250 kg (the heavier payloads being restricted to kamikaze flights iirc, but maybe the land-plane variant with conventional landing gear could carry them, I don't know).

[aizenns 3,591]

10 minutes ago, Z3r0_ said:

It's been suggested before, and I still support it, even its maximum payload would be a bit anemic at 250 kg (the heavier payloads being restricted to kamikaze flights iirc, but maybe the land-plane variant with conventional landing gear could carry them, I don't know).

At least when attack Ulithi, Submarine captains think it is not Kamikaze attack so 800 kg bomb/ torpedo loads is not Kamikaze load. Perhaps pilots hope Kamikaze but designer and commander did not think so.

 

Using such a high-cost plane for Kamikaze is not economical, and they also need recon result of US fleet that attack Japanese main land.

Edited July 4, 2019 by aizenns

[Z3r0_ 4,128]

59 minutes ago, aizenns said:

At least when attack Ulithi, Submarine captains think it is not Kamikaze attack so 800 kg bomb/ torpedo loads is not Kamikaze load. Perhaps pilots hope Kamikaze but designer and commander did not think so.

 

Using such a high-cost plane for Kamikaze is not economical, and they also need recon result of US fleet that attack Japanese main land.

 

Even if it wasn't necessarily a suicide attack with the intent of dying, jettisoning the floats to carry that ordinance would mean having to ditch in the ocean, which would still be a one-way trip in practice at least for the plane, whether they were attacking Ulithi or the Panama Canal.

Also, the cost of the plane didn't really factor into whether a plane was expended in suicide attacks in practice.  Pretty much the only planes that to my knowledge were never used intentionally in such attacks were J2Ms, Ki-84s, and N1Ks, since they were too important for air defense, but planes up to and including medium bombers were still stuffed full of explosives and rammed into American ships.

Edited July 4, 2019 by Z3r0_

[aizenns 3,591]

56 minutes ago, Z3r0_ said:

 

Even if it wasn't necessarily a suicide attack with the intent of dying, jettisoning the floats to carry that ordinance would mean having to ditch in the ocean, which would still be a one-way trip in practice at least for the plane, whether they were attacking Ulithi or the Panama Canal.

Also, the cost of the plane didn't really factor into whether a plane was expended in suicide attacks in practice.  Pretty much the only planes that to my knowledge were never used intentionally in such attacks were J2Ms, Ki-84s, and N1Ks, since they were too important for air defense, but planes up to and including medium bombers were still stuffed full of explosives and rammed into American ships.

Yes, it remove float so it cannot return to carrier, but they planning to return pilot by parachute. This is same as Hurricanes on British “CAM-ship” so it doesn’t mean it is suicide attacker. (Of course pilots will do Kamikaze when attack Ulithi )

 

Edit: reason of why J2M or N1K-J did not do Kamikaze is they did not have enough cruise range: it was only intercepter. Also Ki-84 used for Kamikaze attack by Shimbu-units.

Edited July 4, 2019 by aizenns

[igeticsu 3,400]

Beautiful machine! Gib!

[Z3r0_ 4,128]

On 03/07/2019 at 23:11, aizenns said:

Yes, it remove float so it cannot return to carrier, but they planning to return pilot by parachute. This is same as Hurricanes on British “CAM-ship” so it doesn’t mean it is suicide attacker. (Of course pilots will do Kamikaze when attack Ulithi )

 

Edit: reason of why J2M or N1K-J did not do Kamikaze is they did not have enough cruise range: it was only intercepter. Also Ki-84 used for Kamikaze attack by Shimbu-units.

 

That too, but generally speaking they preferred to expend worn out, obsolete airframes first.

[VWGolf4_20v_AGU 132]

+1

[thealphaoverseer 7]

+1 yes please. Sometimes i need to torpedo someone, so i use my b5n. Sometimes, i need to cap, so i use my n1k. Sometimes I need to torpedo someone occupying the cap, so i take my h8k. It doesn't go so well...

[Miki_Hoshii 2,449]

+1 for probably the greatest single engine float bomber that could be added to WT

[Z3r0_ 4,128]

On 28/01/2020 at 08:41, Miki_Hoshii said:

+1 for probably the greatest single engine float bomber that could be added to WT

 

Eh...there's better ones out there, but this is the best Japan's got.

[leroyonly 4,311]

Suggestion passed to the developers for consideration.