Designations & Abbreviations | Japan

Common designation schemes

Type-designation

Most if not all Japanese military equipment since the Meiji restoration are designated by their adoption year. Depending on the period, they either go off the Calender, Japanese Calender, Or Emperor Period.

• Japanese Imperial Year: Starts with the founding of Japan in 660 BC.
• Japanese Era Name: Nengō (年号) Literally “year name” are names given to (usually) reign periods of Japanese Emperors.
• Shisaku number: After the shift of using Nengō years, the navy re-adopted the use of nengō for their prototype planes to distinguish commissioned prototypes from adopted models.

Examples (Year — Designation Year):

• Type 11 37 mm infantry support gun (1922 — Taishō 11)
• Type 97 Medium Tank “Chi-Ha” (1937 — 2597)
• 12-Shi Carrier-Based Fighter (1937 — Shōwa 12)
• Type 74 MBT (1974)

Order and variants

A repeating pattern in Japanese vehicle designations (and outside of it in both civil and military use) are the Heavenly Stems and the Iroha.

Variants | Heavenly Stems

The Heavenly Stems is a system of ordinals originating in China and widely used across East Asia. During the Shang dynasty, it served as the names for the ten days of the week.

Within the Japanese militaries of WWII, this system was adopted for designating (typically minor) variations of various equipment, functioning similarly to the Western “Mark A/B/C” classification.

More extensively upgraded equipment is often designated with “Kai” (改) or “Kaizen” (改善) to signify large-scale improvements.

Examples:

• Ki-84 Kō / Otsu / Hei
• A6M5b Model 52 Otsu
• Type 4 Kō APHE (75 mm)
• Type 97 Chi-Ha Kai
• N1K2-Ja “Shiden Kai” Model 21 Kō

Order Sequence | Iroha

The Iroha is a famous Japanese poem known for being a perfect pangram, containing each character of the Japanese syllabary exactly once. Because of this, it was used as an ordering system for the syllabary, similar to how the Latin alphabet follows the sequence A, B, C, D…

The Imperial Japanese Army primarily used the Iroha system for tank designations (explained further below), along with occasional applications to other equipment. The Imperial Japanese Navy also employed it for submarine classification.

Imperial Japanese Army

Aircraft (IJA)

The Imperial Japanese Army used two primary designation systems for its aircraft. The more widely known system in the Western world is the Kitai (Ki) index, which assigned a numerical designation to every Army aircraft project upon approval for development or commissioning by the Army High Command. This system functioned similarly to the Soviet “Object” designation for tanks.

Aircraft that were officially adopted into service received a full Type designation, as was common for Japanese military equipment. These designations typically followed the standard format “Type XX [Role]”, with small variants identified with the Heavenly stems and larger remodels separated by Model.

Ki — Kitai: Airframe number/index

• Ki-10 — Type 95 Fighter
• Ki-43-II — Type 1 Model 2 Fighter
• Ki-102b — Type 4 Otsu Assault Aircraft

Tanks (IJA)

The first three adopted Japanese tanks were designated only by order of the Iroha without a role, while other tanks were subdivided by role and order with Iroha:

• Type 89 I-Go — 1st model of the Imperial Japanese year 2589 (1929)
• Type 95 Ro-Go — 2nd model of the Imperial Japanese year 2595 (1935)
• Type 95 Ha-Go — 3rd model of the Imperial Japanese year 2595 (1935)

Example:

Imperial Japanese Navy

Aircraft (IJN)

In the late 1920s, the Navy adopted a short designation naming scheme to indicate the role and manufacturer of the plane next to their standard type designation.

• Standard Type Designation: Type 90 Carrier Fighter
• New Short Designation: A2N (Carrier Fighter — 2nd Type — Nakajima)

After 1929, the long designation got additional information with model designation to indicate variant information, the first number for fuselage/wing changes, the second number for engine, and an optional third letter to signify armament changes

First letters (role)

Second letters (manufacturers/designers)

Official name designation

After July 1943, adopted planes got a name and variant number instead of a full type and model designation.

(ex. [N1K1] “Kyōfū 11” vs [A6M2] “Type 0 Carrier Fighter Model 21”)

Vessels (IJN)

• Carriers — names related to flying animals, actual or mythological

• Battleship — provinces, or alternate names of Japan

• Battlecruisers and heavy cruisers — mountains

• Light cruisers — river names

• Training cruisers — Shinto shrines
• Destroyers — weather, wind, tide, current, wave, moon, season, other natural phenomena, plants
  

• Torpedo boats — birds

• Gunboats — places of scenic beauty and historic interest
• Coast defence ship/Escort ships — islands
  

• Submarines — number sequence starting off the Iroha

• Submarine tenders — whales
• Seaplane tenders — abstract noun, idiomatic word, notable achievement vessels in past war(s)
  

Gun Manufacturer/Designer

Initially imported or license-built weapons were designated by the manufacturer, but would later be simplified under the standardized Japanese Navy convention

ホ — HO: Hotchkiss (FR)

• 13.2 mm/99 "HO" Type → Type 93 13.2 HMG

ヒ/ビ — HI / BI: Vickers (UK)

• 7.7 mm/94 (0.303") "HI" Type
• 12 mm/62 (0.50") "HI" Type → Type 12 Single-barreled MG
• 40 mm/62 (1.575”) “HI” Type → Type 91 40 mm AA

ル — RU: Lewis (UK)

• 7.7 mm/87 (0.303") "RU" Type → Type 92 7.7 mm LMG

カ — KA: Canet (FR)

• 12.6"/38 (32 cm) “KA” Type → 32 cm Type 41

アン — AN: Armstrong (UK)

• 12"/45 (30.5 cm) “AN” Type → 30 cm Type 41
• 12"/50 (30.5 cm) “AN” Type → 30 cm Type 41

コク — KOKU: Krupp (DE)

Japanese Self-Defense Forces (JSDF)

Aircraft (JASDF)

The naming conventions for JSDF aircraft were originally established on April 16, 1974, under directive 防装航第1725号. After multiple revisions, the current regulations are outlined in 防装庁（事）第31号, issued on June 3, 2019.

The system is primarily based on the U.S. military aircraft designation system (MDS), meaning that the structure of letters and numbers used in JSDF aircraft designations follows a similar pattern to the U.S. system.

(2|3) Mission Role:

• C: Cargo (輸送機)
• E: Electronic Warfare (電子戦機)
• F: Fighter (戦闘機) — Example: F-1
  
• K: Tanker (空中給油)
• L: Liaison (連絡機)
• M: Mine Sweeper (掃海)
• O: Observation (観測)
• P: Patrol (哨戒機)
• R: Reconnaissance (偵察機)
• S: Anti-Submarine (対潜機)
• T: Training (練習機) — Example: T-2
• U: Utility (救難、捜索又は多用途)

(3+) Particular Aircraft Type

• H: Helicopter (ヘリコプター)
  
• S: Seaplane (飛行艇)
• V: VTOL (ティルトローター機)
• G: Glider (グライダー)

Tanks (JGSDF)

Prototype designations

From two years after the start of the JSDF (1956) until the 1980s, the JGSDF used 2 letter code prototype codes starting at SS and going further alphabetically:

• SS — Experimental Tracked Armored Vehicle → Type 60 SPRG
• ST(A) – Experimental Medium “Special Vehicle” → Type 61 MBT
• ST(B)  → Type 74 MBT
• ST(C)* → Type 90 MBT*
• SU — Experimental Armored Transport → Type 60 APC
• SU(B) → Type 73 APC
• SV – Experimental Self-Propelled Mortar → Type 60 SPM (81 mm)
• SW – Experimental Mine-Disposal Vehicle
• SX – Experimental Self-Propelled Howitzer → Type 60 SPM (107 mm)
• SY – Experimental Self-Propelled Gun → Type 56 SPH (105 mm)
• SZ – Experimental Special Transport Vehicle

Vessels (JMSDF)

• Helicopter destroyers and Helicopter carriers (DDH) — traditional provinces and mountains
• Guided missile destroyers (DDG) — mountains and weather terms
• Small destroyers (DD) — weather terms
  

• Frigates (DE) — rivers (*initially weather terms)

• Submarines (SS) — ocean currents and legendary auspicious animals
• Replenishment oilers (AOE) — lakes
• Amphibious transport docks and Troopships (LST) — peninsulas