Machinery Technician (MK) is an enlisted rating in the United States Coast Guard that is responsible for the operation, maintenance and repair of a cutter's propulsion, auxiliary equipment and outside equipment, internal combustion engines (gasoline, diesel, gas turbines), environmental support systems (heating, ventilation, air conditioning), hydraulics, generator sets, and areas of hazardous material recovery and control.

They are also responsible for the engineering maintenance of any small boats assigned to their command.

[1] Senior MK's are assigned supervisory positions as shop supervisors at shore installations.

On smaller cutters and at small boat stations senior MK's are assigned as engineer petty officers and are responsible for the overall management of the unit engineering department including its personnel.

The rating of machinery technician includes the obsolete Coast Guard ratings of engineman (EN), machinist mate (MM), Machinery repairman (MR), and Boiler technician (BT).