Growth margin is the key requirement for a future warship

What is the most important requirement for a future warship?

Growth margin: enough unused space and flexibility to add, remove, and rearrange systems throughout the ship's life.

Spare space allows equipment to be added or removed without reorganising the ship around every change. Designs packed to the last millimetre leave little room for that work. A larger Type 45 could have carried its intended equipment while retaining expansion space. Instead, spaces reserved for equipment omitted from the initial fit became the room available for later additions.