Generally speaking, the areas of expertise for Machinist’s Mates (MMs) can be divided into three categories of machinery and equipment—propulsion, auxiliary, and weapons—that are designated by their Service Ratings (MMA, MMN, MMW) And it is no exaggeration to say that a U.S. Navy ship would soon be dead in the water without their expertise and skill.
Sailors holding the basic MM rating could, with a bit of tongue in cheek, be called steampunks. If something on a ship is powered directly or indirectly by steam, it falls under their bailiwick.
Naturally, the largest of these systems is the steam turbines that serve as the power source for the ship’s propellers, but the steam plants that provide propulsion are also used to generate electrical power via turbo-generators, and provide pressure for pump systems.
Additionally, Machinist’s Mates are responsible for the maintenance of auxiliary equipment that is essential to almost every aspect of shipboard life, such as air-conditioning systems, refrigeration plants (including water cooling), water drainage machinery, laundry and galley equipment, steering gears, and, perhaps most important of all, distillation plants. The poet Coleridge’s memorable line—“Water, water, everywhere, nor any drop to drink”—is a reminder of the critical importance of maintaining supplies of potable water.
The handling and disposal of hazardous materials associated with the maintenance and repair of various types of machinery is another duty of Machinist’s Mates. To prevent problems from arising in the first place, they inspect and clean the containers holding any hazardous materials, as well as verify that the containers are properly stowed in areas designated for those materials. Should any type of contamination occur, they take steps to ensure spill containment before executing clean-up procedures. Chief Machinist’s Mates are in charge of monitoring programs designed to control any possible environmental pollution.
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