The designation of "Sea Duty billet" refers to positions that involve assignments on sea-going vessels or with forces that primarily operate at sea. The essential characteristic of these billets is that they typically require personnel to be stationed on ships or directly support naval operations at sea.
The Surface Fleet includes numerous ships, submarines, and aircraft carriers, where personnel directly engage in maritime operations. The Fleet Marine Force operates in conjunction with naval forces and is often deployed on ships, supporting sea-based operations. Navy Mobile Construction Battalions, also known as Seabees, conduct construction and engineering work that frequently requires deployment in maritime settings.
Ground Support Units, however, are primarily focused on activities that are conducted on land. These units support military operations and logistics but do not typically involve sea or maritime operations. Therefore, they do not count as Sea Duty billets. Understanding this distinction from sea-based assignments is crucial for recognizing the nature of various roles within naval forces.