The progress of artillery gave rise to 20-25 cm armor, which turned out to be impossible to protect the entire hull. It was necessary to sacrifice the freeboard at the ends and limit the armor to the belt along the waterline and the central battery, which now housed the artillery. The length of such a battery continued to decrease to compensate for the constant increase in the weight of the armor plates. As already noted, on the Ocean, laid down in 1865, the armor was 17.7% of the displacement, on the Richelieu, laid down in 1868, 19.3%, but to what value can the weight/protection proportion evolve? .Redoutable reached 28%, Devastation 27%, but this is due to the use of steel.