The MM Rating
Originally established as the Finisher rating in 1880, then renamed Machinist in 1884 only to be reverted back to the Finisher rating in 1895, then ultimately given the name that stuck, in 1904, Machinist's Mate. Additionally, the Boiler Technician (BT) rating merged with the Machinist's Mate rating on October 1, 1996.
Machinist's Mates (non-nuclear) 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 generate and stow industrial gases. (Nuclear Machinist's Mate Information)
Machinist's Mate class "A" school is approximately 9 weeks long. The school is located in Great Lakes, Illinois. Machinist's Mate (Submarines) class "A" school is nine weeks in duration, and the school is located in Groton, Connecticut.
Released December 18, 2012, NAVADMIN 382/12 articulates the realignment of the MM and EN ratings.
Machinist's Mate (MM)
The duties performed by Machinist's Mates include aligning piping systems for oil, water, air and steam, and controlling the operation of ship boilers and steam turbines used for ship propulsion and service systems. They control the operation of turbogenerators used to produce electrical power.
MMs clean, adjust, test and perform other preventive maintenance on a ship's boilers, main engines, turbogenerators, and other auxiliary machinery including steering engines, elevators, winches, pumps and associated valves. They operate and maintain desalinization plants (distilling plants) to make fresh water from sea water, and maintain refrigeration plants, air conditioning systems and galley equipment.
MMs repair and replace valves, pumps, heat exchangers, compressors, steam turbines and hydraulic or pneumatic control devices. They also maintain and analyze machinery operating records and reports.
Career Sea - Shore Rotation Chart
Sea tours and shore tours for Sailors that have completed four sea tours will be 36 months at sea followed by 36 ashore until retirement.
Qualifications, Interests, and Working Environment
Machinist's Mates should have clear speech, physical stamina, manual dexterity and the ability to work with others as a team. They should know how to use common hand and power tools and enjoy working with mechanical devices. Other helpful characteristics are resourcefulness and an interest in learning new ideas and skills.
Normal hearing is required. Normal color perception is not required. Members of the MM rating are not required to be citizens of the United States unless a submarine volunteer.
Machinist's mates work within the hull of a ship in fire rooms, boiler rooms, engine rooms or shops. These locations are sometimes hot and noisy. MMs may be required to perform some heavy physical work. They must be able to work closely with others and, in some cases, with limited supervision. MM ASVAB Test score requirements.
The American Council on Education recommends that semester- hour credits be awarded in the vocational certificate or lower-division bachelor's/associate's degree categories for courses taken in this rating on machinery maintenance, blueprint reading, air conditioning and refrigeration.