YouTube / Not What You Think
Vertical Launch Systems have a modular design that provides flexibility on the combination of armaments that a warship can launch. But what happens when a ship equipped with VLS has fired all its missiles?
If you thought that it would have to go back to port and reload, then you got it right.
This is done because of two reasons: First, a large crane is needed to transport the VLS cells into the system. Second of all, stability is required when reloading the huge cells. Neither of these things are available in the middle of the ocean – or in battle.
Earlier VLS modules did have a collapsible crane built-in to assist with reloading, but it was later deemed impractical and dangerous.