Machinist’s Mate (MM) – U.S. Navy Rating

Quick Facts

• Rating Name: Machinist’s Mate
• Abbreviation: MM
• Established: 1880
• Specialty: Ship propulsion and mechanical systems
• Insignia: Two crossed machinist’s hammers
• Modern Context: Includes nuclear propulsion, gas turbines, and auxiliary systems

Insignia of the Machinist’s Mate (MM) Rating. | GGA Image ID # 2362503df3

Overview

The Machinist’s Mate (MM) rating is one of the oldest and most vital in the U.S. Navy. Originating formally in 1880, the rating has spanned over a century of naval service. MMs have been responsible for maintaining and operating the Navy’s mechanical, propulsion, and auxiliary systems across all ship types—from steam-driven battleships of World War I to today’s nuclear-powered carriers and submarines.

Duties

• Operate and maintain ship propulsion systems (steam, diesel, gas turbine, nuclear, depending on era).
• Maintain pumps, compressors, turbines, and auxiliary mechanical equipment.
• Oversee shipboard repair shops and machine tools.
• Assist with maintenance of heating, air conditioning, and water systems on larger ships.
• On submarines, operate key propulsion and auxiliary systems in confined environments.

Specialties Within the Machinist’s Mate Rating

• MM - Machinist's Mate
• MM/SS - Machinist's Mate - Submarine Qualified
• MM/SW - Machinist's Mate - Surface Qualified
• MM(A) - Machinist's Mate (auxiliary)
• MM(A)(GE) - Machinist's Mate (A) (bombing)
• MM(A)(H) - Machinist's Mate (A) (hydrogen)
• MM(A)(P) - Machinist's Mate (A) (Photographic)
• MM(CBE) - Machinist's Mate (construction battalion) (equipment operator)
• MM(MB) - Machinist's Mate (motor boat)
• MM(N) - Machinist's Mate (nuclear)
• MM(O) - Machinist's Mate (optician)
• MM(SRE) - Machinist's Mate (ship repair) (engine operator)
• MM(SRI) - Machinist's Mate (ship repair) (instrument maker)
• MM(SRO) - Machinist's Mate (ship repair) (outside machinist)
• MM(SRS) - Machinist's Mate (ship repair) (inside machinist)
• MME - Machinist's Mate (engineman)
• MMG - Machinist's Mate (industrial gas generating)
• MML - Machinist's Mate (general)
• MMR - Machinist's Mate (refrigeration mechanic)
• MMS - Machinist's Mate (shop mechanic)
• MMARS - Machinist's Mate (arm regulation squad)

Editorial Note: Some specialty designators are historical and no longer in use.

Machinist's Mate Rating and Rank

• MMCM: Machinist's Mate Master CPO | Master Chief Petty Officer
• MMC: Machinist's Mate CPO | Chief Petty Officer
• MM1: Machinist's Mate First Class | Petty Officer, First Class
• MM2: Machinist's Mate Second Class | Petty Officer, Second Class
• MM3: Machinist's Mate Third Class | Petty Officer, Third Class
• MMSN: Machinist’s Mate Seaman | (E-3)
• MMSA: Machinist’s Mate Seaman Apprentice | (E-2)
• MMSR: Machinist’s Mate Seaman Recruit | (E-1)

Historical Context

World War I (1917–1918): MMs worked aboard steam-driven ships, operating complex triple-expansion engines and early turbines.

World War II (1941–1945): Expanded dramatically as the fleet grew, with MMs maintaining propulsion on everything from destroyer escorts to carriers. Many earned combat distinction keeping damaged ships running during battle.

Cold War Era (1947–1991): MMs adapted to nuclear propulsion systems aboard submarines and aircraft carriers, requiring advanced training in nuclear engineering at specialized Navy schools.

Modern Navy: Today’s Machinist’s Mates continue to work with nuclear propulsion, advanced gas turbines, and modern auxiliary systems, making this one of the Navy’s most technically demanding ratings.

Insignia

The traditional MM insignia features two crossed machinist’s hammers, symbolizing technical skill and mechanical expertise.

Relevance for Researchers

Genealogists: Identifying a family member as an MM can open research paths into service aboard specific ship classes or training schools.

Students & Teachers: MMs highlight the evolution of naval technology, from steam power to nuclear propulsion.

Historians: MMs provide a case study in how naval engineering kept pace with global military and industrial changes.

Related Ratings

• Engineman (EN) – focused on diesel engines and auxiliary machinery.
• Boilerman (BT) – operated and maintained shipboard boilers (merged into MM in 1996).
• Gas Turbine Systems Technician (GSM/GS) – specialized in gas turbine propulsion systems.
• Nuclear Propulsion (MMN) – Machinist’s Mates qualified in nuclear power plants, primarily submarines and carriers.

Note: Over time, many mechanical/engineering ratings were merged into Machinist’s Mate as the Navy streamlined propulsion and auxiliary specialties.

Cite This Page

Chicago Style
Gjenvick-Gjønvik Archives. "Machinist’s Mate (MM) – U.S. Navy Rating." GG Archives. Last modified September 2025. https://www.ggarchives.com/MIL/USN/Reference/Ratings/MachinistsMate.html

APA Style
Gjenvick-Gjønvik Archives. (2025, September). Machinist’s Mate (MM) – U.S. Navy Rating. GG Archives. https://www.ggarchives.com/MIL/USN/Reference/Ratings/MachinistsMate.html

MLA Style
Gjenvick-Gjønvik Archives. "Machinist’s Mate (MM) – U.S. Navy Rating." GG Archives, September 2025, https://www.ggarchives.com/MIL/USN/Reference/Ratings/MachinistsMate.html

Student Citation (Simplified)
GG Archives. *Machinist’s Mate (MM) – U.S. Navy Rating*. https://www.ggarchives.com/MIL/USN/Reference/Ratings/MachinistsMate.html