Which term describes a waterborne unit of the fleet not classified as a service craft that can operate independently?

The term that accurately describes a waterborne unit of the fleet not classified as a service craft that can operate independently is "Navy boat." This designation encompasses a variety of vessels that are capable of independent operation and are not limited to a specific role or function within the fleet structure. Navy boats are often designed for a range of missions, including transportation, surveillance, and logistical support, allowing them to be versatile within naval operations.

In contrast, combat craft typically refer to vessels specifically armed or designed for combat operations, while support craft are intended for specific logistical or ancillary roles, such as replenishment or maintenance. Utility vessels, on the other hand, may be specialized for particular tasks but do not broadly encompass the range of operational capabilities afforded by the classification of Navy boat. Thus, "Navy boat" best fits the description provided in the question.