United States military aero engine designations

The United States military aero engine designation system was introduced in 1926, originally for piston engines it was expanded in the 1947 to include a separate system for turbine and rocket engines.

Piston engines
A piston engine designation has three separate elements, a type prefix, a number representing engine displacement and a model number.


 * Type Prefix
 * The type prefix is based on the engine disposition:

Some early engines had the type letter prefixed by a modification letter
 * G - geared
 * I - inverted
 * S - supercharged


 * Displacement
 * A number related to the engine displacement within 5 cubic inches.

Letters were used between 1926 and 1933 then suffixes were numerals with odd number for Army and later Air Force engines and even numbers for Navy engines. After 1943 the letters AN were included to indicate the engine met both Army/Air Force and Navy requirements. Some engines fitted with water-injected engines had the W added to the suffix.
 * Model Suffix

For example the Curtiss V-1150-1 is a Vee-type engine with a displacement of 1150 cubic inches and is an Army model.

Turbine engines
A turbine engine designation consists of four separate elements in the format TSS-MM-NN where T is the type letter, SS is the sequence number, MM is the manufacturer designation (one or two characters), and NN is the model number:


 * Type letter

The prefixes X for experimental and Y for service test are used.


 * Sequence number
 * Each type has its own sequence which started at 30.


 * Manufacturer designation


 * Model number
 * Odd numbers for the United States Air Force and even numbers for the United States Navy

For example the J79-GE-10 is a Turbojet built by General Electric and is a Navy model.

Rocket engines
Have a similar system to turbine engines but use three basic types:

The prefixes X for experimental and Y for service test are used.