How did the "official" Japanese designations work?

I don't know how the Japanese assigning of "official" designations works. If the Kawanishi project was started before Nakajima's but took much longer to come to fruition than the G8N, might it have received a later designation (G9K) from the navy? In other words, does the designation come once the project leaves the drawing board and is approved for a prototype or is it done sometime earlier than that?

windswords said:

I don't know how the Japanese assigning of "official" designations works. If the Kawanishi project was started before Nakajima's but took much longer to come to fruition than the G8N, might it have received a later designation (G9K) from the navy? In other words, does the designation come once the project leaves the drawing board and is approved for a prototype or is it done sometime earlier than that?

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For any given year, there was usually one competition per mission, although in a few cases a disappointing set of proposals could lead to the drafting of a new tender in the same year. For our first example, let us take the Aichi AM-19 (E13A "Jake"). A competition or tender was designated as follows:

• The "-Shi" designation preceded by a number (12-Shi corresponded to the 12h year of the system)
• The description of the type requested (Three-Seat Reconnaissance Seaplane)

Not all design proposals received a designation. Typically a series of designs was submitted by various manufacturers, but only the selected design(s) received a designation.

• The first letter indicated the mission (E = Reconnaissance Seaplane)
• The first number indicated the competition (E13 = 13th Reconnaissance Seaplane competition of the Navy)
• The last letter indicated the manufacturer (E13A = Aichi contender for the Navy's 13th land-based fighter competition)
• The second number indicated the sub-version or variant, "1" being the default number (E13A1 = first variant of the E13A)

PLEASE NOTE : no hyphens or dashes anywhere! Hyphens only existed after the first four digits IF there was a change of mission:

• The letter after the hyphen indicated the new mission assigned to the type (E13A1-K = Reconnaissance Seaplane Trainer)

Sometimes two or three designs proved of interest, so they all received a designation until the winning design among them was chosen. Let's take a second example: the 8-Shi Reconnaissance Seaplane:

• Aichi submitted two designs, the AB-7 biplane and the AM-7 monoplane variant,
• Kawanishi submitted the Type P,
• Nakajima submitted the Type MS.

Other contenders might have existed but they are not known. The AM-7 was rejected straightaway and did not get a designation. The other three received the designations E8A, E8K and E8N and were evaluated, until the Navy opted for the latter one and procured it as its Type 95 Reconnaissance Seaplane or E8N1 (codenamed "Dave" by the US).


Now to go back to your question, if the two designs had been submitted to the same tender AND selected by the Navy for evaluation, they would have had the same middle number, regardless of the delay in producting the prototype. If (and only if) a "G9K" really existed, it was Kawanishi's contender for a hypothetical "9th land-based bomber competition", which we know nothing about.

Stargazer,


That was a superb explanation of how the Japanese navy aircraft designation system worked. Most of us know about the letter code designating the type of aircraft (A for carrier fighter, J for land based fighter, G for land based bomber etc.). And most of know about the manufacturer letter code. But I did not know that the number in the middle did not have to be unique. I, like a lot of others I suppose thought that the middle number represented the number of that type of aircraft regardless of the manufacturer. For instance the A5M and A6M from Mitsubishi would be the 5th and 6th carrier fighters accepted by the navy. Next came the A7M, but I always thought if Nakajima had produced a carrier fighter at the same time and for the same specification it would have to be A8N for the 8th navy carrier fighter. Now I realize that in such a scenario it would A7N.

So Hikoki is right, you cannot have the G9K come after the G8N if the specification for the G9K came before the G8N.

Thank you a such a detailed and well laid out explanation!

Thanks a lot Frank. It was a challenge to keep it clear and to the point, so I'm really glad if it works.

The IJN system was logical on the whole. There were a few exceptions though, which I'd like to address here, hoping some more educated forum members can provide a suitable explanation for each of them...



The L class (transport) saw a jump from L4_ (the Mitsubishi L4M "Topsy" Type 0 Transport) to L7_ (the 13-Shi Small Amphibious Transport competition led to the Nihon L7P but it was rejected). Whatever happened to the L5_ and L6_ slots?



The Aichi AM-24 was submitted to the 17-Shi Experimental Special Attack Aircraft tender and became the M6A Seiran. This is a particularly troubling allocation not only because it was the only aircraft known in the M Experimental class, but also because in all logic in should have been the M1A. Why start at N°6?

Only explanation I can come up with is that the M class succeeded to the D class. The D class spawned a string of attack/dive bomber designs :

• the Aichi D1A "Susie" (which won over the Yokosuka D1Y),
• the Nakajima D2N and Yokosuka D2Y (none of which was procured),
• the Aichi D3A "Val" (which won over the Mitsubishi D3M project and Nakajima D3N),
• the Yokosuka D4Y Suisei, or "Judy" and an unbuilt special attack project,
• the Yokosuka D5Y project.

Why switch from "D" to "M" is beyond me, but at least it would provide a suitable explanation to the number "6." Thoughts, anyone?




Two foreign types were procured in small numbers circa 1938 (the Heinkel He 112B-0 and the Seversky 2PA-B3), and received the designations A7He1 and A8V1. If these designations belonged in the A class for Shipborne Fighters, just after the A6M "Zeke" (the famous "Zero"), why was the much later Mitsubishi M-50 Reppū receive the A7M designation, not A9M?



Foreign evaluations used a parallel system whereby the middle number was simply replaced by the letter "X". This led to AX_, BX_, CX_, DX_, HX_ KX_ and LX_ designations. However, in three cases the designations seem to have been duplicated:

• AXV1 is said to have applied to the Vought Corsair Shipborne Fighter biplane in 1929, and also to the Vought V-143 Experimental Fighter about a decade later.
• LXG1 was both the Tokyo Gas Power KR-2 Special-purpose Liaison Transport of 1934 (which is weird considering it was a local type) but also the single Grumman Amphibious Seaplane, a G-21 Goose imported in 1939.
• LXJ1 applied to two different Junkers designs, a Ju 160 in 1935 and a Ju 86 two years later.

I would appreciate any thoughts on the above remarks!

Stargazer2006 said:

The L class (transport) saw a jump from L4_ (the Mitsubishi L4M "Topsy" Type 0 Transport) to L7_ (the 13-Shi Small Amphibious Transport competition led to the Nihon L7P but it was rejected). Whatever happened to the L5_ and L6_ slots?

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Maybe the L5 and L6 designations were reserved (but never used) for the G5N2-L and G6M1-L2? Or maybe the 13-Shi Small Amphibious Transport plane received the number L7 - not L5 or L6 - to avoid confusion with G5N2-L and G6M1-L2?

Stargazer2006 said:

Two foreign types were procured in small numbers circa 1938 (the Heinkel He 112B-0 and the Seversky 2PA-B3), and received the designations A7He1 and A8V1. If these designations belonged in the A class for Shipborne Fighters, just after the A6M "Zeke" (the famous "Zero"), why was the much later Mitsubishi M-50 Reppū receive the A7M designation, not A9M?

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Maybe because the A7He1 and A8V1 were both removed from service until the Reppu occured?


Letter M was designation for the Tokushu-ki (特殊機) - special (purpose) plane, not Experimental in sense "prototype" or "test plane". I agree that designation M6 was successor of D5.


Regards,

LAW

Stargazer2006 said:

The Aichi AM-24 was submitted to the 17-Shi Experimental Special Attack Aircraft tender and became the M6A Seiran. This is a particularly troubling allocation not only because it was the only aircraft known in the M Experimental class, but also because in all logic in should have been the M1A. Why start at N°6?

Only explanation I can come up with is that the M class succeeded to the D class. The D class spawned a string of attack/dive bomber designs :

• the Aichi D1A "Susie" (which won over the Yokosuka D1Y),
• the Nakajima D2N and Yokosuka D2Y (none of which was procured),
• the Aichi D3A "Val" (which won over the Mitsubishi D3M project and Nakajima D3N),
• the Yokosuka D4Y Suisei, or "Judy" and an unbuilt special attack project,
• the Yokosuka D5Y project.

Why switch from "D" to "M" is beyond me, but at least it would provide a suitable explanation to the number "6." Thoughts, anyone?

Click to expand...

It was indeed a continuation of the D = Carrier Bomber numbering sequence. "D6A" and "M1A" were alternate proposals for a designation. Link to my website http://www.hud607.fire.prohosting.com/uncommon/reference/japan/special_seaplane.html
I'll have to dig up my actual source for this, I think it was in "Monogram Close-Up 13: Aichi M6A1 Seiran: Japan's Submarine-Launched Panama Canal Bomber."
I believe the "X" IJN designation was used for aircraft that were Experimental or Imported for Research (used with another designation).

It was indeed in "Monogram Close-Up 13: Aichi M6A1 Seiran: Japan's Submarine-Launched Panama Canal Bomber." Pages 27-28 detail the process at which the M6A1 designation was arrived. The initial proposal was D6A1: "Since the weapon delivery method of Seiran was originally dive-bombing, the established 'D' designation for 'Carrier Dive Bomber' was considered." However: "This met with opposition. Considering the aircraft configuration, the chief planner for this attack on the Panama Canal insisted that the Seiran should be E17A1, falling in numerical sequence with the twin-floated Paul." Also: "It was the opinion of Vice Admiral Misawa Wada, Chief of Yokosuka Navy Research and Development Arsenal, that the designation 'MXY6' was most appropriate. This, too, met with controversy, as many felt that this would place the Seiran in a class of test vehicles developed at Yokosuka, which up to this point consisted mainly of target gliders and miscellaneous test types." This naturally led to suggesting "M1A1" as the designation (for Special Mission), but it was thought that this could be confused with the already-existing MXY1: "...persons associated with the MXY1, 2, 3, etc. aircraft during their existence would refer to them with the shortened term M1', M2', etc." Finally, we have: "D6A1 was felt the rightful designation by Seiran's chief designer, Mr. Norio Ozaki, and was further endorsed by Rear Adm. Jiro Saba, Chief of the Airframe Section, Yokosuka Naval Arsenal. Considerable debate was generated over which designation to use, and thus a compromise was agreed upon. In light of the 'Special Plane' type, the 'M' was substituted and used in place of the 'D.'" Thus we arrive at M6A1. Incidentally, the same book indicates that the Aichi model number was AM-24.

Thank you all for pointing to the Monogram Close-Up number! It certainly does confirm my assumption.

As for the L5_ and L6_ mystery in the 1937-1939 time range, and after giving the matter some hard thinking, I have come up with a likely explanation (although I have no means of verifying it).

Two Transport Experimental (LX_) designations were duplicated (LXG and LHJ):

• LXG was first used for the Gasuden KR-2 (an unlicensed copy of the De Havilland DH.83) in 1934, but was then reused in 1939 for the Grumman G-21 Goose.
• Similarly, LXJ was first allocated to the Junkers Ju 160 in 1935, then two years later was reassigned to the Junkers Ju 86.

It seems logical to me that once the first LXG and LXJ were procured in small numbers and serviced, they could have been assigned a paper designation as L5G and L6J, enabling Grumman's G-21 and Junkers's Ju 86 to receive the now free slots of LXG and LXJ.

Any thoughts?

List of pre-1945 aircraft, by manufacturer: http://www.hikotai.net/aircraftpre45.htm

by mission: http://www.hikotai.net/aircraftpre45des.htm

I have a few also ;D
http://www.hud607.fire.prohosting.com/uncommon/reference/japan/index.html

https://en.wikipedia.org/wiki/Japanese_military_aircraft_designation_systems

i have found it !