Fan motor units specified herein are intended for ventilation and air conditioning applications only on board ships and craft of the United States Navy. Direction of airflow into and out of the fans is radial. Fans are of nonsparking construction. Fans with motors rated for 149°F ambient temperature are standard, except for type O fan which has an air turbine.

Type CC and X-CC fans are high efficiency units intended for systems having a resistance above 0.6 inch H₂O and up to 1.74 inches H₂O for the smallest fans and above 1.0 inch H₂O and up to 5.3 inches H₂O for larger fans. Type CC fans are nonsparking and shockproof. Type X-CC fans are nonsparking with service C motor.

Type O fan, available in a single size (rated at 750 ft /min and 3.0 inches H₂O static pressure), is intended for emergency cooling of equipment and ventilation of nonventilated spaces. It is always used with ventilation hose, which may be attached to the fan inlet or outlet, or both ends. Exterior surfaces of the fan are of aluminum to avoid sparking when bumped against steel bulkhead.