Which of the following is true about a "Shellback"?

A "Shellback" refers to a sailor who has successfully crossed the equator by ship. This term is part of naval tradition and carries a ceremonial significance, often involving a rite of passage known as the "Line Crossing Ceremony." During this ceremony, sailors celebrate their transition from "pollywog" (those who have never crossed the equator) to "Shellback." Achieving Shellback status is a point of pride within naval culture, representing experience and the completion of a significant milestone at sea.

The other choices do not accurately describe what a Shellback is. For example, those who have never been to sea would not be considered Shellbacks, as crossing the equator by ship is a prerequisite. Additionally, a Shellback is not defined by their role as a naval training officer, nor do they serve mainly on land, as the term specifically pertains to those who have endured the maritime experience of crossing the equator.