One ship is often unavailable during refit, so a singleton capability may disappear whenever maintenance is required. Two ships usually keep one available, but damage or loss immediately reduces the force to that fragile condition. With four, five, or six ships, a navy can sustain deployments, maintenance, and surge capacity while accepting somewhat more risk in each individual design. A larger Nelson class could therefore have traded some armour for speed because losing one of six would be serious rather than strategically devastating.
Notable Point · 1:35:55-1:38:15
Why class size changes acceptable design risk
The conclusion turns the Nelson example into a procurement lesson: a two-ship class must protect each hull more heavily because one loss can erase an available capability.