Sentinel's working career introduces a force-planning rule: fleets need more hulls than the number they intend to deploy at one time. Maintenance and other commitments may leave only about one-third of a class immediately available. Twice the required number might assemble a full force at the start of a war, but attrition and refits would soon reduce it. Three times the requirement can sustain a task group more reliably, while four times provides a deeper margin against losses. If four cruisers must remain in service, a fleet of twelve can sustain that commitment through moderate losses, while sixteen can absorb much heavier attrition before the commitment becomes unsustainable.
Notable Point · 23:05-25:43
Why four available cruisers may require twelve
Two-, three-, and four-times force ratios explain why maintenance, refits, and losses make a nominal order of battle very different from a continuously available force.