Nelson's design made efficient use of the available tonnage because only two units would be built. Scarcity made each hull disproportionately important to the Royal Navy's heavy-gun force. A programme of four or six ships could have justified a faster battleship balance. Class size was itself a design input because availability and acceptable loss changed with the number of hulls ordered.
Chapter · 39:05-39:30
Why two Nelsons demanded an unusually protected design
Because the Royal Navy could build only Nelson and Rodney, it sought maximum protected fighting power in each scarce capital ship rather than the balance appropriate to a larger class.