Why vertical-launch cells are difficult to reload at sea

Why can navies replenish carriers at sea but not simply reload a warship's vertical-launch system?

Modern missiles must be lowered into exposed cells with far greater precision than robust shells, while ship motion, wind, and limited handling equipment make damage likely.

The limitation is a major fleet-sustainment problem that cannot be solved by improvising a crane once war begins. A missile's electronics, actuators, and control surfaces tolerate less rough handling than traditional ammunition. Earlier shipboard VLS cranes consumed cells and reportedly damaged an unacceptable proportion of the weapons they loaded, so the United States Navy stopped fitting them. Using helicopters would place large aircraft close to sensitive radars, while assembling missiles from smaller sections would demand extra crew, protected storage, and dedicated workspace. Arm launchers fed from internal magazines were easier to replenish, but the speed and saturation-defence advantages of VLS drove fleets into a system that currently sends an empty ship back to port.