Magazine depth is a recurring lesson of modern war

What major lesson from earlier wars is repeatedly forgotten in modern naval planning?

Forces need depth: enough ships, weapons, and layered magazines to sustain combat rather than relying on a small number of high-technology systems.

Force depth and magazine capacity are lessons repeatedly lost between wars. Cost-driven reductions in weapons can leave a ship dependent on too few systems even when each individual system is sophisticated. A hypothetical fully armed Type 45 illustrates outer and inner missile layers, medium guns, close-in weapons, and the value of placing them for different fields of fire. Every historical fit need not be copied, but drones and saturation threats make layered volume of fire meaningful. A ship designed around a narrow expected threat can expose weaknesses when the threat changes.