Why a permanent deployment needs several ships

How many ships of a class are needed to keep a deployment going?

Use roughly three ships for a sustained rotation, four for a long unbased deployment, and potentially fewer with effective forward basing.

The answer uses the familiar rule of three as a starting point: one ship deployed, one returning or refitting, and one training or travelling to replace it. A moderate-range commitment can therefore consume three hulls even though only one remains on station. Long-distance deployments without forward bases can require four, while effective forward basing may reduce the rotation burden. Smaller ships can also need more numerical depth because their crews and support facilities are less self-sufficient.