Nuclear-qualified Machinist’s Mates — typically designated MM(N) or simply MM following nuclear power training — operated and maintained the secondary steam plant systems on US Navy nuclear-powered submarines (SSN and SSBN) and aircraft carriers (CVN). After completing Nuclear Power School at Goose Creek, South Carolina and prototype reactor plant training at one of the Navy’s land-based prototype plants, nuclear MMs were assigned to nuclear vessels where their primary watch station was the engine room — the after compartment (in submarines) or the engine room (on surface ships) containing the main propulsion turbines, turbo-generators, and secondary steam system equipment.

Engine Room Watch Station and Asbestos Exposure

Nuclear Machinist’s Mates stood watch in the engine room of nuclear-powered vessels, in direct and sustained proximity to secondary steam system equipment:

  • Secondary steam piping from the steam generators to the main turbine sets — covered with asbestos block insulation in nuclear vessels built before the mid-1980s asbestos phase-down, including USS Enterprise (CVN-65) and the early Los Angeles class submarines (SSN-688 through approximately SSN-725)
  • Main propulsion turbine casings — nuclear MMs monitored main turbine operation and performed turbine maintenance in the engine room where asbestos-insulated turbine casings were present in earlier nuclear vessels
  • Turbo-generators and auxiliary turbines in the engine room — nuclear MMs maintaining ship’s service electrical power systems worked with asbestos-insulated auxiliary turbine equipment in the engine room of early nuclear vessels
  • Auxiliary steam system components — feedwater heaters, steam traps, and auxiliary steam connections throughout the engine room used asbestos-containing packing and gaskets in early nuclear vessel construction

Prototype Training Plant Exposure

Nuclear MM candidates who trained at the Navy’s land-based prototype reactor plants — S1C prototype in Windsor Locks, Connecticut; S5G prototype in Windsor Connecticut; S8G prototype in Ballston Spa, New York; and the Hanford N-reactor site — trained on reactor plants with secondary steam systems using the same asbestos insulation as operational nuclear vessels. Prototype training exposed nuclear MM trainees to asbestos in secondary steam components before their first shipboard assignment.

Enterprise and Early CVN Exposure

USS Enterprise (CVN-65), commissioned 1961, and the early Nimitz class carriers (CVN-68 through approximately CVN-71) were built with asbestos in secondary steam system insulation and interior construction. Nuclear MMs assigned to these carriers’ engineering plants stood engine room watches in direct proximity to asbestos-insulated secondary steam components throughout their carrier engineering tours.

Submarine Nuclear MM Exposure Concentration

In the enclosed submarine engineering environment, nuclear MMs stood watch in the engine compartment for hours-long watch periods in a fully enclosed space without external ventilation. The sustained proximity to asbestos-insulated steam components in the submarine engine compartment, combined with the enclosed atmosphere, created a more concentrated asbestos exposure environment than comparable surface ship watch station duty.

VA Claims for Nuclear MM Veterans

VA presumptive service connection under 38 CFR § 3.309(d) covers asbestos exposure for Navy nuclear engineering personnel. Nuclear Machinist’s Mates who stood engineering watches in nuclear vessels built before the mid-1980s asbestos phase-down and have since been diagnosed with mesothelioma, asbestosis, or asbestos-related lung cancer may qualify for VA disability benefits.