Why a destroyer's single gun does not settle a cruiser layout

Why did the United States develop a single automatic eight-inch gun mount in the first place?

It was tested for destroyer use, where one heavy gun could make sense; a cruiser carrying many such mounts raises different questions about duplicated machinery and space.

The automatic eight-inch gun was a real weapon tested on a destroyer, although the panel disputes how many mounts later designs might carry. A single mount can make sense when a destroyer needs only one heavy gun. Repeating that installation across a cruiser duplicates rotating machinery and consumes space that could carry other weapons. Developing a twin is proposed as an alternative, but the existing mount lacks that capability and would require further design work. The fifth or sixth single eight-inch turret must therefore justify its place against additional anti-aircraft armament.