mtb IJN Type Otsu motor torpedo boats, Emergency warfare type (T21, T25, T-31 ~ T39, T14 and T15)

[aizenns 3,591]

乙型魚雷艇

Type Otsu Motor Torpedo Boat

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No.241 Torpedo boat (No.201 class / project number T-38)

Choushi, March 1944

In this photo it equip 13.2mm machine gun

History

Type Otsu (乙型 / Otsu-Gata, means Type B) torpedo boats is Japanese most-popular torpedo boats.

In 1942, US army landed to Guadalcanal, and Japanese need small torpedo boats to fight US PT-boats. They plan to build lots of small torpedo boat "Otsu-gata" immediately.

When design type of ship, they use IJA Kuchiku-tei "Ka-Ro" because in that time Army has more experience about high-speed vessels since 1920s. (For example, in 1937 Army build "Torpedo chaser" for Navy using design of "HB-K" recon boat). Ka-Ro is wooden boat, but some Otsu-class use steel for its hull.

 

They wanted to equip Mark 71 model 6 engine (Copy of Isotta-Fraschini engine of MAS), but it was difficult to product enough, so they mount used aircraft engines.

First production model of Mk.71 mod.6 is build February 1943, but until October its production result is 3~4 per months: accuracy of there machine tools, jig, and Inspection gauge it too low.

Production of it was cancelled in February 1945 because they don't have enough aluminum. At last they product 340 engines.

 

They use water-cooled engines preferentially, but lots of boats use air-cooled engines (Kinsei, Myousei, Kotobuki etc). Air-cooled engines need cooler fan so need to use about 20% of engine power.

Because of equip used engines, some boat did not reach planned speed. Those boats called "Kaminari-Tei"(雷艇) and used for factotum boat.

Also they plan Hayabusa-tei. This is motor gunboat that remove torpedo dropper from Otsu-class or copy MAS-tei that import from Italy.

 

In totally they build 497 Type Otsu MTB and Hayabusa-class MGB, but include Rai-tei (Torpedo launch) and not-completed one it reach about 800 boats.

 

These boats were deployed on "突撃隊" (Totsugeki-tai, Assault group. NOT means Sturmabteilung) or units of each naval bases.

Totsugeki-tai is coastal defense boats unit that equip Torpedo Boats, Suicide Boats, Suicide Torpedoes, Suicide Divers and Type 4 Special etc.

 

In game

In game, this boat will be Rank I torpedo boat.

Especially, IJN's most produced torpedo boat, No. 538 class (T-14) already in game but it will be first or second vessel.

 

Weapon is 2x 45cm torpedo dropper, 1x machine gun on bridge and depth charges. This boat is very small, so it crew is only 7.

Machine gun is 13.2mm or 25mm, and it speed is lower than 38-knots (≒70 km/h).

Reached to 38 kt is only T-35 (No.468), and other one with two engine is lower than 30 knots!

This means, these boat ate Slow, Weak Weapon, and tiny. It will be bit hard to fight in game.

 

Specification

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Design number	T23	T25	T31	T32	T33	T34	T35	T36	T37	T38	T39	T14	T15
Officially Classified	No.201 class	No.469 class	No.208 class	No.301 class	No.220 class	No.235 class	No/468 class	No.411 class	No.327 class	No.241 class		No.538 class
Material of hull	Steel / Wood	Wood	Steel / Wood	Steel / Wood	Steel / Wood	Wood	Wood	Wood	Steel / Wood	wood	Wood	Wood	Wood
Form of Hull	V-shaped												1 stepped
Built since	1943											1944	1944
Length overall (m)	18.000											15.000	15.206
Width (m)	4.300											3.650	3.800
Depth (m)	2.000											1.600	1.800
Draft (m)	0.650	0.650	0.733	0.737	0.737	0.729	0.742	0.728	0.740	0.734	0.742	0.621	0.686
Displacement (tons)	25.440	25.440	24.000	24.200	24.500	24.000	24.500	24.000	24.000	24.700	24.500	14.500	15.000
Displacement (tonnes)	23.078	23.078	21.772	21.953	22.226	21.772	22.226	21.772	21.772	22.407	22.226	13.154	13.607
Speed (knots)	17	21.5	20.0	21.5	21.0	27.5	35.0	21.5	25.0	27.5	27.0	33.0	35.0
Cruise range (Miles-Knots)	310-14		340-18.5	300-14.5	300-14.5	250-26	240-33	300-24	250-24	225-26	220-25.5
Type of engine (+ is air-cooled)	Type 91, 600 HP	Type 71 mod.6	Hispano Suiza 650HP	Type 91 600 HP	Lorraine 800HP	Type 71 Mod.6	Kotobuki Type 3 +	Myojo Type 2 +	Kinsei Type 41 +	Shinten Type 21 +	Shinten Type 21 +	Type 71 mod.6	Type 71 mod.6
Number of engine	1	1	2	2	2	2	2	2	2	2	2	1	1
SHP	150	920	800	1000	900	1400	1840	860	1200	1400	1440	920	920
Crew	7
Armaments	1×13.2mm / 25mm single machine gun 2× 45cm torpedoes						1× 25mm single machine gun 2× 45cm torpedoes					1× 13mm / 25mm 2× 45cm torpedoes

*T14 is already in game

T25, T28, T35, T31, T33, T34 class are similar design. (they use water-cooled engine)

T36, T37, T38 T39 class are similar design. (they use air-cooled engine, so they have large air intake)

 

Photos

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No.401 torpedo boat (No.201 class / project number T-23)

Sasebo Arsenal, 1943

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No.248 class torpedo boat (project number T38), February 1945, Maizuru

No.248 class torpedo boat (project number T38), Choushi port, Chiba-pref.

No.248 class torpedo boat (project number T38) drawing

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No.449 torpedo boat (No.411 class, T36)

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No.879 class torpedo boat (T14), after war

This model have already in game.

 

Document

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Reference: Blueprint of Hull of "Ka-Ro"

Spoiler

 

 

 

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Sources

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Japan Administrative Division, 2nd Demobilization Bureau (April 25, 1947) "Japanese Naval Vessels at the End of War"

This is official document about Japanese warships to report to USA. (2nd Demobilization Bureau is former Ministry of Navy)

This document published at this website　http://navgunschl2.sakura.ne.jp/tenji/19-IJN_EndOfWar.html

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History and specifications

Society of Naval Architects of Japan (1977) "History of shipbuilding in showa era vol.1" Hara-Shobou publishers

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Photos

Editorial department of magazine "Maru" (1990) "THE IMPERIAL JAPANESE NAVY vol.14 Small Vessels II" Kojin-sha publishers

 

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Photos, history and specifications

Yoshinobu Imamura (2003) "Stories of Japanese Torpedo boats - War history and technology of high speed boats of Japanese Navy" Kojin-sha publishers

 

 

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Blueprint of Ka-Ro for reference

JACAR ref.C14020254500

カロ艇　線図 (Ka-Ro tei Lines)

 

JACAR ref.C14020254400

第２図　駆逐艇（カロ艇）線図　（被板外）  (Kuchikutei (Ka-Ro tei) lines (Outside))

 

Edited December 1, 2018 by aizenns
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[leroyonly 4,311]

Open for discussion. 

[onemax9000 1,243]

No.235 class (T33)

No.235 class (T-34)

No.468 class (T35)

Hint you added (-) just a miner mistake.

 

[Tasty95215 2,099]

After playing Japan's naval forces for a while, I will say that the single 25mm gun on the T-38 is surprisingly powerful and easy to aim, so I think these MTB's won't be too bad in War Thunder. Out of all of these, the one I'm hoping for the most is the T35, since as it's the fastest one by a fair margin at 35 knots. This is especially important considering the current T-38's top speed is incorrect, and will probably be nerfed soon: 

The only thing about the T-35 is that there don't seem to be any pictures of it, just a sketch from the American document shown above. It's unlikely that Gaijin will want to add it, since the lack of pictures will make it difficult to model. The T-15 also has a high top speed, but again there aren't any pictures of it and its stepped hull.

 

Also, even though the speed fo the T-35 is listed as 35 knots in the American document, I have seen it listed as 38 knots instead on a couple of websites(https://ja.wikipedia.org/wiki/乙型魚雷艇 and http://military.sakura.ne.jp/navy/o_pt_otu.htm). Is that accurate?

[aizenns 3,591]

1 hour ago, Tasty95215 said:

After playing Japan's naval forces for a while, I will say that the single 25mm gun on the T-38 is surprisingly powerful and easy to aim, so I think these MTB's won't be too bad in War Thunder. Out of all of these, the one I'm hoping for the most is the T35, since as it's the fastest one by a fair margin at 35 knots. This is especially important considering the current T-38's top speed is incorrect, and will probably be nerfed soon: 

The only thing about the T-35 is that there don't seem to be any pictures of it, just a sketch from the American document shown above. It's unlikely that Gaijin will want to add it, since the lack of pictures will make it difficult to model. The T-15 also has a high top speed, but again there aren't any pictures of it and its stepped hull.

 

Also, even though the speed fo the T-35 is listed as 35 knots in the American document, I have seen it listed as 38 knots instead on a couple of websites(https://ja.wikipedia.org/wiki/乙型魚雷艇 and http://military.sakura.ne.jp/navy/o_pt_otu.htm). Is that accurate?

That document written by 第二復員局, former 海軍省, not a American document. It using English because it is report for GHQ.

T-35 is water-cooled engine model of Type Otsu MTB, so it’s des is same as other Type Otsu MTB with water-cooled engines. 

This is a photo of T-33, one of the Type Otsu MTB that same as T-35.

 

I think that speed data from 昭和造船史 Vol.1. I don’t know which is correct...

Edited July 23, 2019 by aizenns

[Milocat 4,857]

I'm always up for more IJN torpedo boats.  +1.

[Borotovas 4,500]

+1

[OKAZAQI 166]

+1

[leroyonly 4,311]

As the n° 241 Ty pe Otsu class Motor Torpedo B oa t has been implemented previously,

 

Moved to Implemented Suggestions.