Pre-nationalization

Prior to the nationalization of Japanese railways in 1906 and 1907, the government-run railways had numbered their steam locomotives only with serial numbers without consideration of the types of the locomotives. From the beginning of the Kobe–Osaka railway in 1874, they allocated odd numbers to locomotives in Tokyo area and even numbers to locomotives in Kobe area, but this was not maintained after the completion of railway between Tokyo and Kobe in 1889. Later, some locomotives, such as Classes A8 and B6 and rack railway locomotives, were renumbered to make groups for easy recognition of classes.

Classes were introduced by Francis H. Trevithick (1850–1931), a grandson of Richard Trevithick employed by the government of Japan for supervision of rolling stock management. He classified the locomotives with one Latin letter (A through Z), which was then expanded to use two letters (AB, AC, AD, and so on).

Later, this simple method was revised to use one letter and one or two digit numerals with consideration of locomotive types. The meanings of the letters were as follows:

• A – Tank locomotives with two driving axles (A1–A10)
• B – Tank locomotives with three driving axles (B1–B7)
• C – Tank locomotives for rack railway (C1–C7)
• D – Tender locomotives with two driving axles (D1–D12)
• E – Tender locomotives with three driving axles (E1–E7)
• F – Tender locomotives with four driving axles (F1–F2)

1909 rule

Following the railway nationalization, in 1909, the railway authority adopted a new system where locomotives were numbered and classified by four-digit numerals. All existing locomotives were reclassified. Numbers 1 through 4999 were allocated for tank locomotives and 5000 through 9999 were allocated for tender locomotives. Here the classes and the numbers acquired a distinct relationship. Locomotives were grouped in numbers and the classes were represented by the earliest number of the group.

• 1–999 – Tank locomotives with two driving axles
• 1000–3999 – Tank locomotives with three driving axles (3900 and after for rack railway)
• 4000–4999 – Tank locomotives with four driving axles
• 5000–6999 – Tender locomotives with two driving axles
• 7000–8999 – Tender locomotives with three driving axles
• 9000–9999 – Tender locomotives with four driving axles

Numbers within a class were serial in principle. When the number overflowed (as in Classes 8620, 9600 and 9900), one digit was added to precede the four digits to make the numbers five digit. Class 18900 (later reclassified as Class C51) was exceptionally five digit from the beginning.

This numbering and classification rule survived the revision in 1928. Non-standard locomotives that joined the national railways by means of purchase of railway companies were numbered in accordance with this rule even after 1928. Locomotives numbered and classified under this rule includes the locomotives used until very last days of JNR steam locomotives in 1970s.

1928 rule

Because the 1909 method were going to overflow, a new rule of numbering and classification came into effect on October 1, 1928. Except for Classes 18900, 8200 and 9900 being reclassified as C51, C52 and D50 respectively, existing locomotives were not reclassified or renumbered. After this revision, steam locomotives are classified and numbered with a Latin letter and numerals.

Example

D51 200

D	51	200
Number of driving axles	Class	Serial number

Unlike electric and diesel locomotives, steam locomotives do not have an indication of the type of power source (steam) in their class names.

Number of driving axles

A letter indicates the number of driving axles. Number of either leading and trailing axles or axles of tenders is disregarded.

• 2 axles – B
• 3 axles – C
• 4 axles – D
• 5 axles – E

Class

Together with the letter representing the number of driving axles, a two-digit numeral following the letter indicates a class. The number distinguishes tank locomotives and tender locomotives.

• 10–49 – Tank locomotives
• 50–99 – Tender locomotives

According to this numbering method, D51 200 means the 200th engine of Class D51, which is a class of tender locomotives with four driving axles.

JNR

The history of diesel locomotives of the Japanese Government Railways started with two classes of German-made locomotives, the diesel-electric Class DC11 in 1929 and the diesel-mechanical DC10 in 1930. The Ministry of Railways numbered them in accordance with the similar rule as it then used for steam and electric locomotives. The Japanese National Railways assumed this rule.

Example 

DD13 1

D	D	13	1
Diesel locomotive	Number of driving axles	Class	Serial number

D

All classes of diesel locomotives begin with the letter "D" for "Diesel".

Number of driving axles

A letter indicates the number of driving axles. Number of axles without power is disregarded.

• 3 axles – C
• 4 axles – D
• 5 axles – E
• 6 axles – F

Class

Together with the letter "D" and the letter representing the number of driving axles, a two-digit numeral following the letters indicates a class. The number distinguishes the locomotives by the maximum speeds.

• 10–39 - Locomotives with maximum speed 85 km/h or less
• 40–49 - Prototypes
• 50–89 - Locomotives with maximum speed exceeding 85 km/h
• 90–49 - Prototypes

Serial number

Same as electric locomotives.

According to this numbering method, DD13 1 means the first engine of Class DD13, which is a class of diesel locomotive with four driving axles and maximum speed 85 km/h or less.

 JR Freight

After the privatization of JNR in 1987, two Japan Railways Group (JR Group) companies created new classes of diesel locomotives. East Japan Railway Company (JR East) classified its new class as DD19 with the JNR rule as it was only a rebuild of DD17, which was built by JNR. On the other hand, Japan Freight Railway Company (JR Freight) built completely new diesel locomotives, which were classified under the new rule with three-digit class names.

Example 

DF200-12

D	F	200	-	12
Diesel locomotive	Number of driving axles	Class		Serial number

Usage of Latin letters is same as the JNR rule. A hyphen is placed between the class number and serial number.

Class

Three digits of numerals are used to indicate classes. The classification by the maximum speed was replaced by the classification by the forms of power transmission and types of electric motors in case of diesel-electric locomotives.

• 100–199 - Diesel-electric locomotives with DC motors
• 200–299 - Diesel-electric locomotives with AC motors
• 300–399 - Other diesel-electric locomotives
• 500–799 - Diesel-hydraulic locomotives

According to this numbering method, DF200-12 means the 12th engine of Class DF200, which is a class of diesel-electric locomotive with six driving axles and AC electric motors.

Example

EF81 95

E	F	81	95
Electric	Number of driving axles	Class	Serial number

E

All classes of electric locomotives begin with the letter "E" for "electric".

Number of driving axles

A letter indicates the number of driving axles. Number of axles without power is disregarded.

• 2 axles – B
• 3 axles – C
• 4 axles – D
• 6 axles – F
• 8 axles – H

Class

Together with the letter "E" and the letter representing the number of driving axles, a two-digit numeral following the letters indicates a class. Originally, the number distinguished the three types of locomotives.

 

• 10–39 - Locomotives with maximum speed 85 km/h or less
• 40–49 - Locomotives for rack railway
• 50–99 - Locomotives with maximum speed exceeding 85 km/h

As a result of a revision, as of 1987, the rule was as follows.

 

• 10–29 - DC locomotives with maximum speed 85 km/h or less
• 30–39 - AC/DC locomotives with maximum speed 85 km/h or less
• 40–49 - AC locomotives with maximum speed 85 km/h or less
• 50–69 - DC locomotives with maximum speed exceeding 85 km/h
• 70–79 - AC/DC locomotives with maximum speed exceeding 85 km/h
• 80–89 - AC locomotives with maximum speed exceeding 85 km/h
• 90–99 - prototypes

Serial number

In principle, serial number begins with 1. However, numbers may be skipped to create subclasses, such as Class EF65 1000 series or Class ED75 700 series.

According to this numbering method, EF81 95 means the 95th engine of Class EF81, which is a class of AC/DC locomotive with six driving axles and maximum speed exceeding 85 km/h.

Out of seven Japan Railways Group (JR Group) companies established in 1987, only Japan Freight Railway Company (JR Freight) has built new electric locomotives. Initially JR Freight continued to built locomotives originally designed by JNR with minor modifications, it created new class of EF200, adopting the new classification rule with three-digit class names.

Example

EH500-10

E	H	500	-	10
Electric	Number of driving axles	Class		Serial number

Usage of Latin letters is same as the 1928 rule. A hyphen is placed between the class number and serial number.

Class

Three digits of numerals are used to indicate classes. The classification by the muximum speed was replaced by the classification by the types of motors.

• 100–199 - DC locomotives with DC motors
• 200–299 - DC locomotives with AC motors
• 300–399 - Other DC locomotives
• 400–499 - AC/DC locomotives with DC motors
• 500–599 - AC/DC locomotives with AC motors
• 600–699 - Other AC/DC locomotives
• 700–799 - AC locomotives with DC motors
• 800–899 - AC locomotives with AC motors
• 900–999 - Other AC locomotives

According to this numbering method, EH500-10 means the 10th engine of Class EH500, which is a class of AC/DC locomotive with eight driving axles and AC motors.