What term is used to indicate the arrival and departure of commanders and other senior personnel?

The term that signifies the arrival and departure of commanders and other senior personnel is correctly identified as "boat gongs." In maritime tradition, boat gongs are a part of the ceremonial signaling used to indicate specific events or movements of high-ranking officials. Gongs provide an audible warning or announcement that is easily recognizable and is traditionally used to command attention on a vessel or within a naval setting.

While other options may relate to signaling or communication in a nautical context, they do not specifically pertain to the formal indication of senior personnel's movements. For instance, boat bells are typically used for navigation and other announcements, while signal flags serve a different purpose of communication at distance but do not have the ceremonial significance associated with the arrival or departure of command personnel. Cannon fire is often associated with saluting or ceremonial displays, but it is not a direct signal of individual arrivals or departures like gongs are. Thus, boat gongs serve a unique and specific function in this context.