MACHINIST'S MATE (MM)
The main propulsion engineering rating — every Navy turbine, reactor steam plant, and hydraulic system runs through an MM.
OVERVIEW
Machinist's Mate (MM) is the U.S. Navy's main propulsion and auxiliary-machinery rating. MMs operate and maintain the gas turbines, steam turbines, reduction gears, freshwater plants, refrigeration plants, hydraulics, and high-pressure air on every U.S. Navy combatant. The rating splits into the "MM (Surface)" general track and the "MM (Nuclear)" track (MMN) that operates pressurized-water reactors on aircraft carriers and submarines.
A general-track MM aboard a destroyer or amphibious ship operates the LM2500 gas-turbine main engines, the auxiliary boilers and freshwater stills, the air-conditioning plants, and the high-pressure-air compressors. Nuclear-track MMs run the reactor compartment and main steam plant on Nimitz- and Ford-class carriers and on every Navy submarine.
The general community covers the U.S. Navy's traditional shipboard ratings — deck, engineering, weapons, and combat-systems Sailors who keep surface combatants and amphibious ships in the fight. Sailors in this community typically rotate between sea and shore tours and are eligible for a wide range of NECs, instructor billets, and enlisted commissioning programs.
A-school for the rating runs ~14 weeks (Surface) / ~6 months Nuclear Power School + Prototype at Surface Warfare Officers School Detachment, Great Lakes, IL (Surface) / Nuclear Power Training Command, Goose Creek, SC (Nuclear), where Sailors complete the technical foundation needed to report to their first fleet command. Entry requires the ASVAB line score VE+AR+MK+AS=200 and an enlistment obligation of 5–6 years. MMs advance through the standard enlisted paygrade structure (E-1 through E-9), competing in the Navy-Wide Advancement Examination (NWAE) at E-4 through E-6 and via the Selection Board at E-7 through E-9. Senior MMs typically serve as Leading Petty Officer (LPO), Work Center Supervisor, Leading Chief Petty Officer (LCPO), or Command Master Chief (CMC), and may pursue Limited Duty Officer (LDO), Chief Warrant Officer (CWO), or commissioning programs such as STA-21, MECP, or OCS.
Across the active force, MM Sailors are essential to the Navy's mission readiness, and the rating remains an in-demand career field with strong reenlistment bonuses (SRB), advancement opportunities, and pathways into Navy Reserve, civilian DoD, and industry careers after service.
WHAT MMs DO
Surface Machinist's Mates operate and maintain the LM2500 gas-turbine main engines on cruisers, destroyers, and frigates, the geared steam turbines on legacy steam ships, the freshwater distillation plants, refrigeration and air-conditioning, hydraulic and steering gear, and the high-pressure air compressors. Nuclear MMs operate the reactor compartment, main steam plant, and feedwater systems on aircraft carriers and submarines, including reactor scram recovery, steady-state power operations, and mid-life refueling overhauls.
RESPONSIBILITIES
- Surface Machinist's Mates operate and maintain the LM2500 gas-turbine main engines on cruisers, destroyers, and frigates, the geared steam turbines on legacy steam ships, the freshwater distillation plants, refrigeration and air-conditioning, hydraulic and steering gear, and the high-pressure air compressors. Nuclear MMs operate the reactor compartment, main steam plant, and feedwater systems on aircraft carriers and submarines, including reactor scram recovery, steady-state power operations, and mid-life refueling overhauls.
- Stand watches and qualify on the rating's Personnel Qualification Standards (PQS), maintain training jackets, and mentor junior MMs as required by the chain of command.
- Lead the MM work center as Leading Petty Officer or Work Center Supervisor — managing maintenance documentation in 3M/MFOM, parts ordering, and personnel qualifications.
- Support general military training (GMT), damage control, force protection, and watch-bill assignments common to every Sailor regardless of rating.
THIS RATING ABSORBED
The MM rating's mission today includes work that flowed from the following decommissioned U.S. Navy ratings:
HISTORY
Machinist's Mate is one of the oldest engineering ratings in the U.S. Navy, established in 1869 as the Navy moved from sail and reciprocating steam to compound engines and steam turbines. Through the 20th century the rating absorbed multiple specialty engineering rates and now stands as the senior auxiliary-machinery and propulsion rating in the surface Navy.
The Nuclear-track MMN sub-rating was established in the 1950s as the Navy commissioned its first nuclear-powered submarine, USS Nautilus (SSN-571), and remains the dominant enlisted rating in the Naval Nuclear Propulsion Program.
Like all surface-Navy general ratings, the rating evolved alongside the U.S. Navy's transition from sail to steam, then steam to gas-turbine and electric-drive propulsion, and continues to adapt to today's distributed maritime operations and integrated combat systems.
Today the Machinist's Mate (MM) rating is overseen by the Enlisted Community Management (ECM) office at My Navy HR and the Center for Personal and Professional Development. Modern MMs benefit from the Sailor 2025 personnel-system reforms, the Ready Relevant Learning (RRL) training continuum, and credentialing through the Navy COOL program — turning rating qualifications into industry-recognized certifications and licenses.
The rating's structure, training pipeline, and operational employment continue to evolve alongside the Navy's transition to Distributed Maritime Operations (DMO), Project Overmatch, and the Force Design 2045 fleet architecture, ensuring MMs remain central to the warfighting mission.
TRAINING PIPELINE
- 1. Recruit Training (Boot Camp)~10 weeksNaval Station Great Lakes, ILInitial entry training for all U.S. Navy enlisted Sailors at the Navy's only boot camp.
- 2. Machinist's Mate A-School~14 weeks (Surface) / ~6 months Nuclear Power School + PrototypeSurface Warfare Officers School Detachment, Great Lakes, IL (Surface) / Nuclear Power Training Command, Goose Creek, SC (Nuclear)Initial rating-skills training for MM accessions.
- 3. Fleet / Operational TourFirst sea or operational tourDDG-51 Arleigh Burke-class destroyersOn-the-job training and qualifications in the MM rating with a fleet unit.
TYPICAL CAREER PATH
- E-1/E-3Apprentice MMA-school then engine-room striker tour; nuclear pipeline runs ~2 years in NPS and at a prototype plant.
- E-4/E-6Petty Officer MMQualify on main propulsion systems, hold engineering watch positions, lead a work-center.
- E-7+Chief Machinist's MateEngineering Department LCPO, Engineering Officer of the Watch, or Reactor Department CPO afloat.
TYPICAL PLATFORMS & UNITS
- DDG-51 Arleigh Burke-class destroyers
- CG-47 Ticonderoga-class cruisers
- Aircraft carriers (CVN-68 / CVN-78)
- Every U.S. Navy submarine (Nuclear MM)
EXAMPLE NECs
- MM-4287 Gas Turbine Auxiliary
- MM-3367 Nuclear Power Plant Operator
- U.S. citizenship and minimum ASVAB VE+AR+MK+AS=200
- High school diploma or equivalent
- Pass the Navy physical and medical screening
- DDG-51 Arleigh Burke-class destroyers
- CG-47 Ticonderoga-class cruisers
- Aircraft carriers (CVN-68 / CVN-78)
- Every U.S. Navy submarine (Nuclear MM)