The modern ten-inch gun offers an analogy for the fourth rate: both appear to occupy an ideal middle ground on paper. Once naval guns grew beyond about 9.2 to 9.4 inches, their rate of fire was much the same as a 12- to 14-inch weapon, while the larger gun delivered the heavier hit. In the same way, a fourth rate carried too little force for the battle line but cost too much to field in frigate numbers. Its apparent balance concealed a procurement compromise that satisfied neither principal role.
Chapter · 2:06-4:10
Why fourth rates sat in an awkward middle ground
Like a seemingly ideal intermediate gun calibre, the fourth rate looked balanced on paper but proved a poor substitute for either line-of-battle ships or frigates.