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Navy Rating · Engineering

MM Machinist's Mate

Current service use not established

This code is listed in the directory. Inclusion alone does not confirm current service use.

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Overview

Machinist's Mates operate, maintain, and repair ship propulsion machinery, auxiliary equipment, and outside machinery. They service boilers, pumps, blowers, and heat exchangers, manage lubricating oils, fuels, and water, maintain records, and generate and stow industrial gases.

Minimum ASVAB: VE+AR+MK+AS 188 or VE+AR+MK+AO 193

ASVAB policy: Not policy-reviewed · coverage unknown · as of 2026-10-19

Program scope has not been reviewed.

Policy applicability and coverage of the program's score routes have not been reviewed. Shown-route arithmetic is not an eligibility decision.

Source: milpersman-1306-618-rating-list-2026-04 (source date 2026-04). Policy applicability has not been established.

See if you would hit this score: free ASVAB practice test

Core Skills

  • Marine boiler and heat exchanger maintenance
  • Fuel, oil, and water testing and transfers
  • Shipboard refrigeration and air conditioning repair
  • Industrial gas generation and storage

Civilian Career Paths

Career associations are editorial assessments of the cited evidence, not an official crosswalk unless the evidence explicitly says so. O*NET supplies civilian occupation information, not proof of a military match. Related experience does not confer civilian qualifications. Tasks and tools below describe civilian work, not military training.

Maintenance and Repair Workers, General

Repairing propulsion machinery, pumps, hoisting equipment, and other shipboard auxiliary equipment transfers directly to equipment-focused maintenance work.

How to prepare: Build a repair portfolio identifying the equipment you serviced, the repairs you performed, and the maintenance records you maintained for applications to machinery-focused maintenance positions.

What the civilian work involves
  • Perform routine maintenance, such as inspecting drives, motors, or belts, checking fluid levels, replacing filters, or doing other preventive maintenance actions.
  • Inspect, operate, or test machinery or equipment to diagnose machine malfunctions.
  • Repair machines, equipment, or structures, using tools such as hammers, hoists, saws, drills, wrenches, or equipment such as precision measuring instruments or electrical or electronic testing devices.

Stationary Engineers and Boiler Operators

Operating and maintaining marine boilers, pumps, forced draft blowers, and heat exchangers closely matches stationary plant equipment work.

How to prepare: Compare your documented boiler experience with the license class covering equipment at plants in your target city or state. Some jurisdictions require experience and a written examination, with each license class limiting the equipment type and size permitted for unsupervised operation.

What the civilian work involves
  • Operate or tend stationary engines, boilers, and auxiliary equipment, such as pumps, compressors, or air-conditioning equipment, to supply and maintain steam or heat for buildings, marine vessels, or pneumatic tools.
  • Monitor boiler water, chemical, and fuel levels, and make adjustments to maintain required levels.
  • Observe and interpret readings on gauges, meters, and charts registering various aspects of boiler operation to ensure that boilers are operating properly.
Civilian tools and software (examples)
  • Building management system software

Heating, Air Conditioning, and Refrigeration Mechanics and Installers

Maintaining and repairing shipboard refrigeration and air conditioning equipment provides directly relevant mechanical experience for civilian HVAC service.

How to prepare: Ask a local HVAC apprenticeship or technical program to assess your shipboard experience and identify gaps in civilian installation and electrical testing. Covered refrigerant work requires passing an equipment-appropriate EPA-approved certification test unless working as an apprentice under close, continual supervision by a certified technician; state or local trade licensing may also apply.

What the civilian work involves
  • Test electrical circuits or components for continuity, using electrical test equipment.
  • Discuss heating or cooling system malfunctions with users to isolate problems or to verify that repairs corrected malfunctions.
  • Connect heating or air conditioning equipment to fuel, water, or refrigerant source to form complete circuit.

Training & Development

Choose credentials for your target role. COOL funding markers describe program listings, not a guarantee of eligibility or funding.

Career Growth

  • Certified Maintenance and Reliability Professionals (CMRP)

    Demonstrate broader maintenance and reliability knowledge when progressing beyond hands-on repair or plant operation.

    Eligibility and preparation: No education or work-experience minimum; candidates must not have taken the exam within the preceding six months.

    For: Maintenance and Repair Workers, General, Stationary Engineers and Boiler Operators

Notes & Sources

Evidence for this guidance (9 documents)
  1. NAVPERS 18068F Vol I (NEOCS, Jan 2026 edition): MACHINIST’S MATE (MM)

    [1] Rating chapter "SCOPE OF RATING"; cached text line 51234; NAVPERS 18068F Vol I, 2026-01 edition

    Supports: Marine boiler and heat exchanger maintenance, Fuel, oil, and water testing and transfers, Shipboard refrigeration and air conditioning repair, Industrial gas generation and storage, Maintenance and Repair Workers, General (O*NET 49-9071.00), Stationary Engineers and Boiler Operators (O*NET 51-8021.00), Heating, Air Conditioning, and Refrigeration Mechanics and Installers (O*NET 49-9021.00)

  2. O*NET: Maintenance and Repair Workers, General

    [2] O*NET 30.3 occupational data

    Supports: Maintenance and Repair Workers, General (O*NET 49-9071.00)

  3. O*NET: Stationary Engineers and Boiler Operators

    [3] O*NET 30.3 occupational data

    Supports: Stationary Engineers and Boiler Operators (O*NET 51-8021.00)

  4. Bureau of Labor Statistics: Stationary Engineers and Boiler Operators

    [4] How to Become a Stationary Engineer or Boiler Operator; Licenses, Certifications, and Registrations; page dated 2026-08-27, retrieved 2026-09-23

    Supports: Stationary Engineers and Boiler Operators (O*NET 51-8021.00)

  5. O*NET: Heating, Air Conditioning, and Refrigeration Mechanics and Installers

    [5] O*NET 30.3 occupational data

    Supports: Heating, Air Conditioning, and Refrigeration Mechanics and Installers (O*NET 49-9021.00)

  6. US EPA: Section 608 Technician Certification Requirements

    [6] Requirements and Types of Certifications; updated July 15, 2026

    Supports: Heating, Air Conditioning, and Refrigeration Mechanics and Installers (O*NET 49-9021.00)

  7. Bureau of Labor Statistics: Heating, Air Conditioning, and Refrigeration Mechanics and Installers

    [7] How to Become; Education and Training; Licenses, Certifications, and Registrations; updated August 27, 2026

    Supports: Heating, Air Conditioning, and Refrigeration Mechanics and Installers (O*NET 49-9021.00)

  8. COOL credential mapping: Certified Maintenance and Reliability Professionals (CMRP)

    [8] MM cached COOL credential feed

    Supports: Certified Maintenance and Reliability Professionals (CMRP)

  9. Society for Maintenance and Reliability Professionals: CMRP eligibility

    [9] Eligibility; retrieved 23 September 2026

    Supports: Certified Maintenance and Reliability Professionals (CMRP)

Defense contractor jobs for MM

Predecessor codes

Historical codes with documented links to MM. Each history page explains the change.

BTBoiler Technician

Descriptions may be summarized for clarity. Verify all information with your branch career counselor or official military documentation before making career decisions.

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