46 CFR 11.502: General requirements for national engineer endorsements.

(a) For all original and raise of grade of engineer endorsements, at least one-third of the minimum service requirements must have been obtained on the particular mode of propulsion for which the applicant seeks endorsement.

(b) If an applicant desires to add a propulsion mode (steam, motor, or gas turbine) to their endorsement while holding an MMC officer endorsement in that grade, the following alternatives are acceptable:

(1) Four months of service as an observer on vessels of the new propulsion mode.

(2) Four months of service as an engineer officer at the operational level on vessels of the new propulsion mode.

(3) Six months of service as Oiler, Boiler Technician/Watertender, or Junior Engineer on vessels of the new propulsion mode.

(4) Completion of a Coast Guard-approved training course for this endorsement.