Why vertical-launch missiles are hard to reload at sea

Could warships reload vertical-launch missiles at sea by using an onboard crane or a helicopter to place rounds near the cells?

Only with substantial handling space and risk. Large missiles, ship motion, nearby sensors, and hazardous helicopter operations make routine underway reloading extremely difficult.

Modern vertical-launch missiles are large, heavy, and difficult to align safely with cells on a moving ship. A permanent crane and handling area consumes deck volume that designers may prefer to use for additional launch cells or other systems. Helicopter delivery would require repeated movements close to radar arrays, communications antennas, the bridge, and personnel handling live weapons. An accident could damage critical equipment or lose both the aircraft and the weapon. At-sea missile replenishment is therefore a fleet-logistics and ship-design problem rather than a simple matter of adding a hoist.