Why replacing Ticonderoga's aft gun with VLS is not simple

Would removing Ticonderoga's aft gun and raising the deck for more VLS have been a better upgrade?

Probably not: the proposed cells face weight and depth constraints, and the gun retains a limited role after the missiles are exhausted.

Replacing the aft gun with VLS raises questions about weight and the depth available for launch cells. Propeller shafts occupy the afterbody, limiting how far a launcher can extend below a raised deck. The initial assessment questions whether the proposed installation would fit and acknowledges uncertainty about the ship's shaft arrangement. A separate reason for retaining the 5-inch gun is that it leaves some defensive capability if a saturation attack exhausts the missiles. Its usefulness in that situation would be limited, but underway missile reloading would not remove the immediate need for a fallback.