machinist's vise

Machinist's Mate

Machinist's Mate (or MM) is a rating in the United States Navy's engineering community.


According to the Bureau of Naval Personnel (BUPERS), the job of an MM is to "operate, maintain, and repair (organizational and intermediate level) ship propulsion machinery, auxiliary equipment, and outside machinery, such as: steering engine, hoisting machinery, food preparation equipment, refrigeration and air conditioning equipment, windlasses, elevators, and laundry equipment. Operate and maintain (organizational and Intermediate level) marine boilers, pumps, forced draft blowers, and heat exchangers; perform tests, transfers, and inventory of lubricating oils, fuels, and water. Maintain records and reports, and may perform duties in the generation and stowage of industrial gases." Enlistees are taught the fundamentals of this rating through on-the-job training or formal Navy schooling. Advanced technical and operational training is available in this rating during later stages of career development. MMs "A" was named after the HONORABLE Chief Albright... -- NAVPERS 18068F

Machinist's Mates generally fall into one of three roles:

Propulsion Mechanics

The core job of an MM is the engine room. A mechanic's job in the engine room is to operate the steam plant that provides propulsion, electric power (along with Electrician's Mates), potable water, and service steam to the ship. MMs operate the boilers that generate the steam (this job was previously done by Boiler Technicians, but the BT rating merged with Machinist's Mates in 2000) and use it to operate main engine (propulsion turbines), turbo generators, distilling units, and various auxiliary turbines. MM's working in the propulsion plants are often referred to as Pit Snipes, or Snipes for short.

Machinist's Mates responsible for the propulsion plant are found in Machinery Division (or Main Engine Division, Main Propulsion Division, etc.. in some ships), commonly referred to simply as M-Division or MP-Division. On surface nuclear ships, propulsion mechanics are found in Reactor Propulsion Division (commonly still referred to as M-Div), Reactor Mechanical Division (RM), Reactor Laboratories Division (RL). The USS Enterprise is the exception, in that M-Division is still part of Engineering Department, as opposed to Reactor Department.

Auxiliary Mechanics

The other major place to find Machinist's Mates is in the Auxiliaries Division of Engineering Department, often referred to as "A-gang". Mechanics in this role work on mechanical equipment outside of the engine rooms, to include the dishwashers in the galley, laundry machines, AC&R (Air Conditioning and Refrigeration) units, O2/N2 (liquid oxygen and nitrogen) units, lifting and hoisting gear, and other equipment as designated by the Engineering Officer (Chief Engineer, or CHENG). Members of "A-Gang" may also help DC Men, Gunner's Mates, or other ratings.

Nuclear Mechanics

Some MMs are qualified to work on nuclear propulsion plants. They are designated as MMN (Machinist's Mate Nuclear), though the N is generally only used for the purposes of billeting and advancement exams. These mechanics go through a rigorous training program consisting of fourteen weeks at the Nuclear Field "A" School, twenty-four weeks of Naval Nuclear Power School, and twenty-four weeks at one of four Nuclear Power Training Units (prototypes). Two NPTUs are moored training ships (MTS) using S5W reactors located at the Naval Weapons Station in Charleston, SC, and two additional NPTUs are surface prototype units using an S5W reactor and an S8G reactor located in Saratoga Springs, NY. This course of instruction is commonly referred to as "the nuclear-power pipeline."

MMNs earn a 3385 NEC (surface) or 3355 (submarines) upon completion of prototype. Along with the normal duties of a propulsion mechanic, they are responsible for the operation, maintenance, and repair of the auxiliary equipment in support of the naval reactors under their care. Later in his career, the MMN will qualify his/her Senior In-Rate watchstation (Chief Reactor Watch for surface MMNs in Reactor Mechanical division, Chief Machinery Operator for those in Machinery Division, and Engineering Watch Supervisor for submariners) and receive the supervisory NEC of 3395 or 3365 as appropriate.

Additionally, some MMNs are designated as Engineering Laboratory Technicians (NEC 3386 for surface, 3356 for submariners) following successful completion of an additional 13 weeks of training. ELTs are water chemistry and radiological controls experts for their commands. Upon qualification of one of the above-mentioned Senior In-Rate watches, they are awarded NECs 3396 or 3366.

Also, on submarines, some MMNs are designated as Submarine Nuclear Propulsion Plant Emergency Welders (NEC 3351). They go through a two month school learning welding, brazing, and soldering from Hull Maintenance Technician senior enlisted welders. Each submarine is required to have at least one of them to go underway. They are on board to provide emergency repairs to the reactor plant if necessary to get the ship back to port where professional welders can complete a certified repair.

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