maritime officer; ship's officer
A licensed professional responsible for navigation, engineering, or communications on a vessel. This is a formal occupational title in Japan.
He obtained a maritime officer's license.
He works aboard a cargo ship as a maritime officer.
航海士 is a navigating officer, a specific type of 海技士. 海技士 is the broader category that includes engineers and other technical officers.
Compound of 海 (sea, maritime) + 技 (skill, technique) + 士 (professional, specialist). The term is a modern occupational title.