The U.S. Navy Machinist’s Mate (MM) Rating
The Machinist’s Mate (MM) rating was the U.S. Navy’s specialized enlisted rating responsible for operating, monitoring, and maintaining the steam turbines, reduction gears, condensers, evaporators, distilling plants, refrigeration plants, hydraulic systems, pneumatic systems, and the vast network of steam-driven and electric-driven auxiliary machinery throughout every Navy ship of the asbestos era. From World War II through today, MMs have stood watch in the engineering spaces immediately adjacent to the ship’s boiler rooms — in the same asbestos-saturated industrial environment as their Boiler Tender (BT) counterparts.
In 1996, the Navy merged the Boiler Tender rating into Machinist’s Mate as part of the engineering-rating consolidation. From that point forward, all U.S. Navy steam-propulsion plant operators have served under the MM designation regardless of whether their assignment is boiler room or engine room.
A career MM spent thousands of hours over a 20-year service career in immediate, hands-on contact with asbestos pipe insulation, asbestos turbine insulation, asbestos block insulation on condensers and evaporators, asbestos gaskets at every flange and manhole, asbestos packing at every pump and valve, asbestos cement, asbestos cloth lagging, asbestos-insulated valves and instruments, asbestos brake and clutch linings on steam-driven auxiliary equipment, and asbestos-bearing distilling plants.
What the Machinist’s Mate did
The MM rating’s core duties spanned every aspect of the ship’s propulsion plant and auxiliary machinery:
- Main propulsion plant operation — main engines (steam turbines + reduction gears + condensers + circulating-water systems)
- Auxiliary machinery operation — auxiliary turbines, electric motors, hydraulics, pneumatics, refrigeration plants, air-conditioning plants
- Distilling plant operation — evaporators, distilling condensers, distillate pumps, and fresh-water production systems
- Auxiliary boiler operation — auxiliary boilers, auxiliary feed pumps, lubricating-oil systems
- Pump operation and maintenance — feed pumps, fire pumps, bilge pumps, fuel-oil service pumps, lube-oil pumps, refrigeration compressors, air compressors
- Steam and water system maintenance — main steam, auxiliary steam, condensate, feed, fresh-water, salt-water, fuel-oil, and lube-oil systems
- Mechanical repair shop work — machining, welding, brazing, gasket fabrication, valve repair, pump rebuilding
- Casualty response — equipment failures, leaks, flooding, fires in machinery spaces
- Repair-yard support during major overhauls
How MM asbestos exposure occurred
Every routine MM duty involved the disturbance, handling, or proximity to asbestos-bearing materials:
- Turbine insulation removal and replacement — main engines, auxiliary turbines, generator turbines — for inspection, repair, or rebuild
- Condenser tube replacement and end-cover gasket replacement — disturbing asbestos block insulation on condenser shells and asbestos gaskets at every penetration
- Evaporator and distilling-plant maintenance — disturbing asbestos block insulation on evaporator shells and asbestos gaskets at every tube-bundle penetration
- Pump gasket and packing replacement — every pump in the machinery space had asbestos gaskets at the flanges and asbestos packing at the shaft
- Valve packing replacement at every valve in the engineering plant
- Pipe insulation removal and re-installation when accessing piping for repair
- Mechanical-room gasket fabrication — cutting and shaping asbestos sheet-gasket material on the machine-shop bench
- Brake and clutch service on steam-driven and electric-driven auxiliary equipment
- Refrigeration compressor service — many refrigeration plants used asbestos-bearing gaskets and insulation
- Bystander exposure to insulators, hull technicians, repair-yard workers, and other ratings working in the same machinery space
Ships where MMs served
MMs served aboard virtually every U.S. Navy ship of the asbestos era — steam-propulsion, diesel-electric, and nuclear-powered — including battleships, all aircraft carrier classes (Essex, Midway, Forrestal, Kitty Hawk, Nimitz, Enterprise), all cruiser classes, all destroyer classes (Fletcher through Burke), all frigate classes (Knox, Garcia, Brooke, Perry), all amphibious classes (LPD, LSD, LHA, LHD, LPH), all submarine classes (fleet boats, Skipjack, Permit, Sturgeon, Los Angeles, Ohio, Virginia, Seawolf), and all auxiliaries (oilers, tenders, repair ships, ammunition ships, cargo ships).
Nuclear-powered submarines had reactor-plant asbestos PLUS steam-plant asbestos in the propulsion turbines and auxiliaries.
For per-ship documentation, see navyshipexposure.com.
Particularly heavy MM exposure tasks
Within the MM trade, several specific tasks are documented in publicly filed U.S. asbestos litigation as among the highest-fiber-release activities of Navy engineering service:
- Turbine “lagging” tear-out — removing and replacing the asbestos thermal insulation jacketing the main and auxiliary turbines, often required during every major overhaul
- Condenser end-cover and waterbox gasket replacement — disturbing asbestos gaskets sealing each end of the main condenser
- Evaporator tube-bundle pulls — disturbing asbestos block insulation and gaskets at the tube-bundle penetrations
- Machine-shop gasket fabrication — cutting asbestos sheet gasket material to fabricate custom flange gaskets, generating respirable dust at the bench
- Reduction-gear maintenance — disturbing asbestos gaskets and packing at the gear-case penetrations
- Bilge and overhead cleaning — disturbing accumulated asbestos fiber that had settled out of the machinery-space atmosphere over years of operation
VA service-connected disability for MM veterans
MM veterans diagnosed with mesothelioma, asbestosis, lung cancer, or other asbestos-related conditions should pursue both VA service-connected disability claims and civil claims against asbestos product manufacturers. Both pursuits are routine and compatible.
If you served as a Machinist’s Mate during the asbestos era
If you served in the U.S. Navy Machinist’s Mate (MM) rating — including post-1996 MMs who served under the consolidated MM designation that subsumed the Boiler Tender (BT) rating — and have since been diagnosed with mesothelioma, asbestosis, lung cancer, or another asbestos-related illness, you may have legal rights.
Free, confidential case evaluation: Speak with O’Brien Law Firm — (314) 936-2956
All consultations are free. No fee unless a financial recovery is made on your behalf.