A fourth rate could not match a 74's line-of-battle power, but it also cost too much to replace frigates in bulk. In 1814 the Royal Navy had roughly 360 sloops and other small vessels in commission because worldwide cruising and patrol work demanded numbers above all. A fleet that tried to replace both third and fifth rates with a single middle type would still need many hulls, but each would cost more and remain inferior in at least one role. In 1794 more second rates than fourth rates were in commission, showing how narrow the middle tier had become. Britain had the resources to build fourth rates in quantity and generally chose not to once it could supply enough specialized battle-fleet and cruising ships. The surviving niche was command of independent frigate squadrons, where only a limited number of leaders was required.
Notable Point · 36:31-42:25
The procurement problem of the fourth rate
As the Royal Navy could afford adequate third rates and fifth rates, the expensive compromise between them became a niche station-flagship type.