Generally the most junior marine engineer of the ship, this person is usually responsible for electrical, sewage treatment (resulting in the pejorativepun "turd engineer"), lube oil, bilge, and oily water separation systems. Depending on usage, they are called "the Third" or "the Fourth" and usually stands a watch and sometimes assists the third mate in maintaining proper operation of the lifeboats.
Maritime academies such as the U.S. Merchant Marine Academy offer a four-year program leading to a BS in Marine Engineering Technology, a license (issued by the Coast Guard) as a third assistant engineer, and an optional commission as ensign in the U.S. Naval Reserve, Merchant Marine Reserve, or Coast Guard Reserve. With experience and additional training, third officers may qualify for higher rank.